improve error strings

this definitely has the potential to be a bikeshed topic, so some
justification is in order. most of the changes made fit into one of
the following categories:
1. alignment with text in posix, xsh 2.3
2. eliminating overly-specific text for shared error codes
3. making the message match more closely with the macro name
4. removing extraneous words

in particular, the EAGAIN/EWOULDBLOCK text is updated to match the
description of EAGAIN (which covers both uses) rather than saying the
operation would block, and ENOTSUP/EOPNOTSUPP is updated not to
mention sockets.

the distinction between ENFILE/EMFILE has also been clarified; ENFILE
is aligned with the posix text, and EMFILE, which lacks concise posix
text matching any historic message, is updated to emphasize that the
exhausted resource is not open files/open file descriptions, but
rather the integer 'address space' of file descriptors.

some messages may be further tweaked based on feedback.

src/errno/__strerror.h

@@ -5,7 +5,7 @@
  * of the strings remains synchronized. */
 
 E(EILSEQ,       "Illegal byte sequence")
-E(EDOM,         "Argument outside domain")
+E(EDOM,         "Domain error")
 E(ERANGE,       "Result not representable")
 
 E(ENOTTY,       "Not a tty")
@@ -15,25 +15,25 @@ E(ENOENT,       "No such file or directory")
 E(ESRCH,        "No such process")
 E(EEXIST,       "File exists")
 
-E(EOVERFLOW,    "Value too large for defined data type")
+E(EOVERFLOW,    "Value too large for data type")
 E(ENOSPC,       "No space left on device")
 E(ENOMEM,       "Out of memory")
 
-E(EBUSY,        "Device or resource busy")
+E(EBUSY,        "Resource busy")
 E(EINTR,        "Interrupted system call")
-E(EAGAIN,       "Operation would block")
-E(ESPIPE,       "Illegal seek")
+E(EAGAIN,       "Resource temporarily unavailable")
+E(ESPIPE,       "Invalid seek")
 
 E(EXDEV,        "Cross-device link")
 E(EROFS,        "Read-only file system")
 E(ENOTEMPTY,    "Directory not empty")
 
 E(ECONNRESET,   "Connection reset by peer")
-E(ETIMEDOUT,    "Connection timed out")
+E(ETIMEDOUT,    "Operation timed out")
 E(ECONNREFUSED, "Connection refused")
 E(EHOSTDOWN,    "Host is down")
-E(EHOSTUNREACH, "No route to host")
-E(EADDRINUSE,   "Address already in use")
+E(EHOSTUNREACH, "Host is unreachable")
+E(EADDRINUSE,   "Address in use")
 
 E(EPIPE,        "Broken pipe")
 E(EIO,          "I/O error")
@@ -48,51 +48,54 @@ E(ENOEXEC,      "Exec format error")
 E(EINVAL,       "Invalid argument")
 
 E(E2BIG,        "Argument list too long")
-E(ELOOP,        "Too many levels of symbolic links")
+E(ELOOP,        "Symbolic link loop")
 E(ENAMETOOLONG, "Filename too long")
-E(ENFILE,       "File table overflow")
-E(EMFILE,       "Too many open files")
-E(EBADF,        "Bad file number")
-E(ECHILD,       "No child processes")
+E(ENFILE,       "Too many open files in system")
+E(EMFILE,       "No file descriptors available")
+E(EBADF,        "Bad file descriptor")
+E(ECHILD,       "No child process")
 E(EFAULT,       "Bad address")
 E(EFBIG,        "File too large")
 E(EMLINK,       "Too many links")
-E(ENOLCK,       "No record locks available")
+E(ENOLCK,       "No locks available")
 
 E(EDEADLK,      "Resource deadlock would occur")
-E(ENOSYS,       "Function not supported")
+E(ENOTRECOVERABLE, "State not recoverable")
+E(EOWNERDEAR,   "Previous owner died")
+E(ECANCELED,    "Operation canceled")
+E(ENOSYS,       "Function not implemented")
 E(ENOMSG,       "No message of desired type")
 E(EIDRM,        "Identifier removed")
 E(ENOSTR,       "Device not a stream")
 E(ENODATA,      "No data available")
-E(ETIME,        "Timer expired")
+E(ETIME,        "Device timeout")
 E(ENOSR,        "Out of streams resources")
 E(ENOLINK,      "Link has been severed")
 E(EPROTO,       "Protocol error")
-E(EBADMSG,      "Not a data message")
+E(EBADMSG,      "Bad message")
 E(EBADFD,       "File descriptor in bad state")
-E(ENOTSOCK,     "Socket operation on non-socket")
+E(ENOTSOCK,     "Not a socket")
 E(EDESTADDRREQ, "Destination address required")
-E(EMSGSIZE,     "Message too long")
+E(EMSGSIZE,     "Message too large")
 E(EPROTOTYPE,   "Protocol wrong type for socket")
 E(ENOPROTOOPT,  "Protocol not available")
 E(EPROTONOSUPPORT,"Protocol not supported")
 E(ESOCKTNOSUPPORT,"Socket type not supported")
-E(EOPNOTSUPP,   "Operation not supported on socket")
+E(ENOTSUP,      "Not supported")
 E(EPFNOSUPPORT, "Protocol family not supported")
 E(EAFNOSUPPORT, "Address family not supported by protocol")
-E(EADDRNOTAVAIL,"Cannot assign requested address")
+E(EADDRNOTAVAIL,"Address not available")
 E(ENETDOWN,     "Network is down")
-E(ENETUNREACH,  "Network is unreachable")
-E(ENETRESET,    "Network dropped connection because of reset")
-E(ECONNABORTED, "Software caused connection abort")
+E(ENETUNREACH,  "Network unreachable")
+E(ENETRESET,    "Connection reset by network")
+E(ECONNABORTED, "Connection aborted")
 E(ENOBUFS,      "No buffer space available")
 E(EISCONN,      "Socket is connected")
-E(ENOTCONN,     "Socket is not connected")
+E(ENOTCONN,     "Socket not connected")
 E(ESHUTDOWN,    "Cannot send after socket shutdown")
 E(EALREADY,     "Operation already in progress")
-E(EINPROGRESS,  "Operation now in progress")
-E(ESTALE,       "Stale NFS file handle")
+E(EINPROGRESS,  "Operation in progress")
+E(ESTALE,       "Stale file handle")
 E(EREMOTEIO,    "Remote I/O error")
 E(EDQUOT,       "Quota exceeded")
 E(ENOMEDIUM,    "No medium found")