Unused function w32_cat_get() in regex

[pjtsu]

I think w32_cat_get() in w32_regex_traits.cpp is unused by regex.
w32_cat_get() calls LoadStringA() and LoadStringW() of USER32.dll.
If w32_cat_get() is deleted, libboost_regex-*.lib can link to just only KERNEL32.dll.

If w32_cat_get() remains, I think revision is necessary.
Destination buffer of WideCharToMultiByte() in w32_regex_traits.cpp may be shortage,
because not a letter of all MultiByte-CodePages are in 2 bytes.
Constant value MB_LEN_MAX should be instead of 2.
MB_LEN_MAX is in <climits> header.

[anonymous]

The functions are potentially called from the header.

I'll change the code to let WideCharToMultiByte itself determine the buffer size.

BTW WideCharToMultiByte is only used on systems with no narrow character Win32 API's such as WinCE.

[John Maddock]

(In [83967]) Fix buffer size determination. Fixes #8082.