gibber-debug.h: wrap macros in parentheses/G_STMT_START as appropriate
gibber-debug.h: wrap macros in parentheses/G_STMT_START as appropriate

This fixes compilation of non-debug builds by making
"if (...) DEBUG (foo); else DEBUG (bar);" no longer provoke a warning.

Also remove empty definition of NODE_DEBUG in non-debug builds (it no
longer exists in debug builds).

Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,community-ssu/telepathy-gabble,community-ssu/telepathy-gabble,jku/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,community-ssu/telepathy-gabble,jku/telepathy-gabble,jku/telepathy-gabble,mlundblad/telepathy-gabble,community-ssu/telepathy-gabble