Disable new -Wstring-plus-int warning where needed for now.
Adjust various places that add GCC-only options to check for the active
compiler first.

Port over NetBSD fixes:
- remove configure hooks to other os's
- handle symlinks in cvsroot
- configurable CVS local directory name
- unlock patch
- setxid patch (handle setuid CVS and drop privilege

Port over NetBSD fixes:
- remove configure hooks to other os's
- handle symlinks in cvsroot
- configurable CVS local directory name
- unlock patch
- setxid patch (handle setuid CVS and drop privileges correctly)
- when __SSP__ avoid alloca
- admin commands in history
- programmable admin group
- always enforce admin group
- protocol independent network handling (handle ipv6)
- correct issue with wrong revision in resurrected files
- centralize cvs password cleanup in memory
- don't segv if we re-enter exit handlers
- more sprintf -> snprintf
- extra empty line in editor buffer
- alias 't' with 'T' in logmsg.c for compatibility
- alias config "LocalKeyword" with "tag" and "UserAdminOptions" with
"AdminOptions" for compatibility.
- disable Checking-prog and Update-prog for security
- take account of our current umask when computing the mode of files.

show more ...