Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Make the malloc(3) family of functions weak and make their non-weak
implementations visible for use by applications. The functions $F that
are now weak symbols are:
allocm, calloc, dallocm, free, malloc, malloc_usable_size,
nallocm, posix_memalign, rallocm, realloc, sallocm

The non-weak implementations of $F are exported as __$F.

Submitted by: stevek@juniper.net
Reviewed by: jasone@, kib@
Approved by: jasone@ (jemalloc)
Obtained from: juniper Networks, Inc

Fix a compilation error with some compilers: __attribute__
requires two parenthesis for its argument, but instead of using
__attribute__ directly, use the appropriate __nonnull macro
from cdefs.h.

Import jemalloc 9ef7f5dc34ff02f50d401e41c8d9a4a928e7c2aa (dev branch,
prior to 3.0.0 release) as contrib/jemalloc, and integrate it into libc.
The code being imported by this commit diverged from
lib/libc/stdlib/malloc.c in March 2010, which means that a portion of
the jemalloc 1.0.0 ChangeLog entries are relevant, as are the entries
for all subsequent releases.

Add __{BEGIN,END}_DECLS macros, so that function prototypes remain
unmangled for C++ programs.

Submitted by: Niklas Sorensson <nik@cs.chalmers.se>

Add malloc_usable_size(3).

Discussed with: arch@