Make error message after failing commit_lock_file() less confusing

The error message after a failing commit_lock_file() call sometimes
looks like this, causing confusion:

  $ git remote add remote git@server.com/repo.git
  error: could not commit config file .git/config
  # Huh?!
  # I didn't want to commit anything, especially not my config file!

While in the narrow context of the lockfile module using the verb
'commit' in the error message makes perfect sense, in the broader
context of git the word 'commit' already has a very specific meaning,
hence the confusion.

Reword these error messages to say "could not write" instead of "could
not commit".

While at it, include strerror in the error messages after writing the
config file or the credential store fails to provide some information
about the cause of the failure, and update the style of the error
message after writing the reflog fails to match surrounding error
messages (i.e. no '' around the pathname and no () around the error
description).
Signed-off-by: NSZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: NJeff King <peff@peff.net>

config.c

@@ -2144,7 +2144,8 @@ int git_config_set_multivar_in_file(const char *config_filename,
 	}
 
 	if (commit_lock_file(lock) < 0) {
-		error("could not commit config file %s", config_filename);
+		error("could not write config file %s: %s", config_filename,
+		      strerror(errno));
 		ret = CONFIG_NO_WRITE;
 		lock = NULL;
 		goto out_free;
@@ -2330,7 +2331,8 @@ int git_config_rename_section_in_file(const char *config_filename,
 	fclose(config_file);
 unlock_and_out:
 	if (commit_lock_file(lock) < 0)
-		ret = error("could not commit config file %s", config_filename);
+		ret = error("could not write config file %s: %s",
+			    config_filename, strerror(errno));
 out:
 	free(filename_buf);
 	return ret;

credential-store.c

@@ -64,7 +64,8 @@ static void rewrite_credential_file(const char *fn, struct credential *c,
 		print_line(extra);
 	parse_credential_file(fn, c, NULL, print_line);
 	if (commit_lock_file(&credential_lock) < 0)
-		die_errno("unable to commit credential store");
+		die_errno("unable to write credential store: %s",
+			  strerror(errno));
 }
 
 static void store_credential_file(const char *fn, struct credential *c)

fast-import.c

@@ -1821,7 +1821,7 @@ static void dump_marks(void)
 
 	dump_marks_helper(f, 0, marks);
 	if (commit_lock_file(&mark_lock)) {
-		failure |= error("Unable to commit marks file %s: %s",
+		failure |= error("Unable to write file %s: %s",
 			export_marks_file, strerror(errno));
 		return;
 	}

refs.c

@@ -4643,7 +4643,7 @@ int reflog_expire(const char *refname, const unsigned char *sha1,
 					get_lock_file_path(lock->lk));
 			rollback_lock_file(&reflog_lock);
 		} else if (commit_lock_file(&reflog_lock)) {
-			status |= error("unable to commit reflog '%s' (%s)",
+			status |= error("unable to write reflog %s: %s",
 					log_file, strerror(errno));
 		} else if (update && commit_ref(lock)) {
 			status |= error("couldn't set %s", lock->ref_name);