Added missing header for OS X
Merge pull request #23 from kyamagu/master

Added missing header for OS X
string: add bson_strfreev().
bson_strfreev: allow NULL parameter.
string: make sure \0 is always set at end of string.
string: add bson_strnlen() for systems without strnlen().
symbols: add bson_strnlen() to ABI.
TestSuite: add ASSERT helpers and include options in test output.
More win32 compat for the mongo c driver