b64: don't downcast to signed char.

fixes assert on win32.
tests: cleanup TestSuite a bit.
tests: win32 fix.
tests: churn.
tests: specify a log file with -F <filename>
tests: log tests to test.log.
macros: use __inline__ for -ansi.
macros: whitespace.
bson: documentation and whitespace cleanup.
clock: support bsds explicitly.
context: general cleanup.

Use BSON_GNUC_CONST to loader can patch in result instead of function call.
General whitespace cleanup.
json: use memset() correctly.
tests: check for HAVE_CLOCK_GETTIME.
clock: include sys/time.h for clock_gettime().
build: set  _POSIX_C_SOURCE before check funcs for clock_gettime.
build: check for clock_gettime using AC_SEARCH_LIBS.
context: docs and whitespace.
thread: various cleanup.
documentation and whitespace cleanup.
error: cleanup bson_strerror_r(), docs.