Forcing libssh2 lib location

OS X may have libssh2 in diff locations, so CHECK_LIBRARY_EXISTS may check the wrong lib; forcing it to use a found directory.

CMakeLists.txt

@@ -286,7 +286,7 @@ IF (LIBSSH2_FOUND)
 	#SET(LIBGIT2_PC_LIBS "${LIBGIT2_PC_LIBS} ${LIBSSH2_LDFLAGS}")
 	SET(SSH_LIBRARIES ${LIBSSH2_LIBRARIES})
 
-	CHECK_LIBRARY_EXISTS("${LIBSSH2_LIBRARIES}" libssh2_userauth_publickey_frommemory "" HAVE_LIBSSH2_MEMORY_CREDENTIALS)
+	CHECK_LIBRARY_EXISTS("${LIBSSH2_LIBRARIES}" libssh2_userauth_publickey_frommemory "${LIBSSH2_LIBRARY_DIRS}" HAVE_LIBSSH2_MEMORY_CREDENTIALS)
 	IF (HAVE_LIBSSH2_MEMORY_CREDENTIALS)
 		ADD_DEFINITIONS(-DGIT_SSH_MEMORY_CREDENTIALS)
 	ENDIF()