core: Improve the debug messages even more.

* src/debug.c (_gpgme_debug): Add arg LINE.  Chnage all callers.
(_gpgme_debug_begin): Remove.
* src/debug.h (TRACE_SEQ): Use the LINE arg of _gpgme_debug.

This includes chnages to always print fds in decimal as weel as
tweaking the TARCE_SEQ function to make use of the new machinery.

The standard 'tag' can now always be NULL and no tag information will
be printed.

• Signed-off-by: Werner Koch <wk@gnupg.org>