[PATCH] Some _l fixes

[Roland McGrath]

I put in strftime_l and wcsftime_l.  However, I noticed a problem.
They use some underlying locale-sensitive functions that have no *_l
versions.  _nl_{get,parse}_* should probably just be replaced with versions
that take the struct locale_data * and have some space in that struct
to cache their state instead of using static variables, which then
needs a local lock.  wcsftime uses mbsrtowc, and there is no mbsrtowc_l.

strptime uses some of the same problematical _nl_* functions.