Implement missing POSIX function nl_langinfo_l

Change nl_langinfo to nl_langinfo_l using locale given as argument.
Remove outdated TRANSITION_PERIOD_HACK.  The codeset is stored in
the locale for quite some time now.  For !MB_CAPABLE targets, just
return "US_ASCII" as codeset.

Implement nl_langinfo by calling nl_langinfo_l.  Export nl_langinfo_l
from Cygwin DLL and bump minor API version number.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/common.din

@@ -939,6 +939,7 @@ nexttowardl NOSIGFE
 nftw SIGFE
 nice SIGFE
 nl_langinfo SIGFE
+nl_langinfo_l SIGFE
 nrand48 NOSIGFE
 ntohl NOSIGFE
 ntohs NOSIGFE