mysql_client.c:gw_client_close didn't close client session in cases where session->state == SESSION_STATE_STOPPING. That is a bug and lead to situation where session wasn't closed at all.

Also changed 'authorization failed' to 'access denied'
mysql_common.c: fixed memory leak in gw_receive_backend_auth, and replaced error code '2800' with '28000'.
readconnroute.c:handleError didn't set *succp pointer so uninitialized value was used in caller's context.
makefile.inc: added -lm to linker flags
mysql_backend.c: added a few comments

makefile.inc

@@ -25,7 +25,7 @@ endif
 # -O2 -g -pipe -Wformat -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fstack-protector --param=ssp-buffer-size=4 -fPIC
 
 CFLAGS      := $(CFLAGS) -Wall
-LDLIBS      := $(LDLIBS) -pthread
+LDLIBS      := $(LDLIBS) -pthread -lm
 LDMYSQL     := -lmysqld
 CPP_LDLIBS  := -lstdc++