basesrc: call _stop when start failed

When we failed to complete the start, call stop again. This makes sure that all
successfull calls to _start are paired with a _stop.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=687845
element: improve debug
add debug category

Adding a debug category is nicer than logging to the default category
docs: update plugin docs

Update args/signals etc.
NEWSEGMENT -> SEGMENT
baseparse: fix invalid output timestamps in some cases
queue2: refactor buffering percent and stats

Make methods to get the current buffering percent and the stats. We will use
this in the query later.
queue2: implement buffering query for all modes

Also implement the buffering query for STREAM mode.
multiqueue: correct overrun handling

The control of wheteher a SingleQueue is full is not correct.
Rewrote single_queue_overrun_cb() so it checks the correct variables
when checking if the queue has reached the hard limits, and to
increase the max buffer limit once for each call.

https://bugzilla.gnome.org/show_bug.cgi?id=690557
systemclock: add OTHER clock type

Add an OTHER clock type so that subclasses are able to mark themselves as
using some other clock source than the realtime or monotonic clock.
docs: update synchronization document a little
bin: add flag to disable resync state change

Add a GST_BIN_FLAG_NO_RESYNC that disables a resync when an element is added,
removed or linked in the bin. This is interesting for complex bins that
dynamically add elements to themselves and want to manage the state of those
elements without interference from resyncs.

See https://bugzilla.gnome.org/show_bug.cgi?id=690420
scripts: fix location of repository with ssh
gstvalue: some micro-optimisations

Avoid unnecessary value copying, and unnecessary init/unset
cycles which all go through the value table. There's a bunch
of places where we copy a value and then unset it in the next
line, instead of just taking over the source value.
caps, structure,  taglist: micro-optimisations

Avoid some unnecessary GValue copying by making use of
gst_structure_id_take_value() where possible.
configure: replace deprecated AM_CONFIG_HEADER with AC_CONFIG_HEADERS

AM_CONFIG_HEADER has been removed in the just-released automake 1.13:
https://lists.gnu.org/archive/html/automake/2012-12/msg00038.html

https://bugzilla.gnome.org/show_bug.cgi?id=690881
basesink: Check if buffers are too late before calling prepare/prepare_list

https://bugzilla.gnome.org/show_bug.cgi?id=690936
adapter: return gssize from gst_adapter_masked_scan_* functions

As the return value of this function is -1 when the match is not found
basesink: Initialize uninitialized variable
docs: minor systemsclock doc fix