Also fix some issues that crept into earlier commits during the conflict
resoution for the rebase.

Delete the following API functions:
- set_dirname()
- with_dirname()
- set_filestem()
- with_filestem()
- add_extension()
- file_path()

Also change pop() to return a boolean instead of an owned copy of the
old filename.

Standardize the is_sep() functions to be the same in both posix and
windows, and re-export from path. Update extra::glob to use this.

Remove the usage of either, as it's going away.

Move the WindowsPath-specific methods out of WindowsPath and make them
top-level functions of path::windows instead. This way you cannot
accidentally write code that will fail to compile on non-windows
architectures without typing ::windows anywhere.

Remove GenericPath::from_c_str() and just impl BytesContainer for
CString instead.

Remove .join_path() and .push_path() and just implement BytesContainer
for Path instead.

Remove FilenameDisplay and add a boolean flag to Display instead.

Remove .each_parent(). It only had one caller, so just inline its
definition there.

Add a new trait BytesContainer that is implemented for both byte vectors
and strings.

Convert Path::from_vec and ::from_str to one function, Path::new().

Remove all the _str-suffixed mutation methods (push, join, with_*,
set_*) and modify the non-suffixed versions to use BytesContainer.

Remove the old path.
Rename path2 to path.
Update all clients for the new path.

Also make some miscellaneous changes to the Path APIs to help the
adoption process.

They've been replaced by putting the name on the extern block.

  #[abi = "foo"]

goes to

  extern "foo" { }

Closes #9483.

This change was waiting for privacy to get sorted out, which should be true now
that #8215 has landed.

Closes #4427

Also, documentation & general clean-up:
- remove `gen_char_from`: better served by `sample` or `choose`.
- `gen_bytes` generalised to `gen_vec`.
- `gen_int_range`/`gen_uint_range` merged into `gen_integer_range` and
  made to be properly uniformly distributed. Fixes #8644.

Minor adjustments to other functions.

FormatMessageA may return non-ascii message,
which is encoded as system code page, not utf8.
This may cause `assert!(is_utf8(v))` failure on
some non-English machines.
This patch replaces it with FormatMessageW,
which returns utf-16 message.

Fixes `make check-stage2-std` failure on my machine. :)

The trait will keep the `Iterator` naming, but a more concise module
name makes using the free functions less verbose. The module will define
iterables in addition to iterators, as it deals with iteration in
general.

fixing issue #6100.

Android has no /tmp partition, return /data/tmp instead. Cf. #8511.

They are still present as part of the borrow check.

Some extern blobs are duplicated without "stdcall" abi,
since Win64 does not use any calling convention.
(Giving any abi to them causes llvm producing wrong bytecode.)

removed pub on real_args, changed test to use args

.with_c_str() is a replacement for the old .as_c_str(), to avoid
unnecessary boilerplate.

Replace all usages of .to_c_str().with_ref() with .with_c_str().

cc #7887