The time come to remove the wrapper, most likely, but tidy up it code
instead for now.  Remove spurious blank line, use C89 definition, wrap
long line.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Add MAP_EXCL flag for mmap(2).  It should be combined with MAP_FIXED,
and prevents the request from deleting existing mappings in the
region, failing instead.

Reviewed by:	alc
Discussed with:	jhb
Tested by:	markj, pho (previous version, as part of the bigger patch)
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Fix compile warning: Remove duplicate external declaration.
Fix GCC compile warning: Variable(s) can be used uninitialized.