- Added first attempt at general caching mechanism (GstTimeCache renamed to GstCache)

- Added first attempt at general caching mechanism (GstTimeCache renamed to GstCache)

Original commit message from CVS:
- Added first attempt at general caching mechanism (GstTimeCache renamed
to GstCache)
- Some more clocking checks and updates (waiting on GST_CLOCK_TIME_NONE
returns immediatly instead of blocking forever)
- Moved clock get/set functions to element class instead of instance.
- Added cache methods on elements.
- Renamed GST_PROPS_BOOL_TYPE to GST_PROPS_BOOLEAN_TYPE to make it more
consistent with gst_props_get/set_boolean and GST_PROPS_BOOLEAN.
- Give short stats about plugins in gst-inspect.