Move GNU_SOUCE definition to configure.ac
Change all headers to use config.h.
Move config.h to the top.
Remove errno.h if it is not needed.

Started looking at the ticket #107 related to
traverse functions. Realized that the return values
are not consistent. That ovelapped with the work
that I wanted to do for ticket #103 - errno cleanup.
So I (across collection, INI and ELAPI):
* Made the return codes consistent (where found)
* Removed errno where it is not needed
While was testing used valgrind and found a nasty
problem when the value was added to collection with
overwriting duplicates the count was decreased improperly.
Fixing collection.c to not decrease count made
valgrind happy. While I was debugging this
I also spotted several build warnings in trace
statements when the " exp ? v1 : v2 " was used.
Fixed those.
In ini_config.c there was a trace stament that used
variable after it was freed. Removed trace stament.

Fix consts and function declarations

Patch prepends prefix "col_" to all
functions related to collection.
This caused some formatiing issues
so the alignement was addressed too.

Patch adds two interfaces for stack and queue using
collection as underlaying implementation.
It also fixes a bug in the insterion code -
the unsigned properties were created as long.