pgsql: Slight speedup in column processing.
Master: Removed erroneous mutex.

This mutex has survived since ~2000, and seems to never have been useful.

In Pike 8.0 and later it could cause a deadlock, due to locking order
together with the compilers internal mutex as used by decode_value():

  Legend:

    CM:	master()->compilation_mutex (now removed).
    IM:	The compilers internal mutex.

  Thread 1:		Thread 2:		Notes:
  ----------------------------------------------------------
  decode_value()
  compile()					Lock IM.
			low_cast_to_program()
			findprog()
			low_findprog()
			CM->lock()		Lock CM.
			compile()		Wait for IM.
  low_cast_to_program()
  findprog()
  low_findprog()
  CM->lock()					Wait for CM.

This bug wasn't triggered before Pike 8.0 as then the compiler
forced threads to be disabled on entry.

FIXME: Do we need to retain the symbol "master()->compilation_mutex"?

Fixes [bug 7366].
pgsql: Preserve type information if PG_DEBUG is defined.
release number bumped to 8.0.34 by export.pike
release number bumped to 8.0.35 by export.pike
pgsql: Avoid race during buffer fill/read.
pgsql: Check for the desired buffer size before returning.
pgsql: Cannot use add_hint() here, the types have already been set in stone.
pgsql: Using howmuch with a sizeof compare of the Buffer does not work.

howmuch is the amount we need extra.  It does not relate to the amount
already in the Buffer.  To prevent a race/deadlock we need extra
signaling.