ext/pulse/: Some smaller cleanup. Use G_PARAM_STATIC_STRINGS, gst_element_class_set_details_simple() and fix coding s...

Original commit message from CVS:
* ext/pulse/pulsemixer.c: (gst_pulsemixer_base_init),
(gst_pulsemixer_class_init):
* ext/pulse/pulsesink.c: (gst_pulsesink_base_init),
(gst_pulsesink_class_init), (gst_pulsesink_prepare):
* ext/pulse/pulsesrc.c: (gst_pulsesrc_interface_supported),
(gst_pulsesrc_base_init), (gst_pulsesrc_class_init),
(gst_pulsesrc_prepare):
Some smaller cleanup. Use G_PARAM_STATIC_STRINGS,
gst_element_class_set_details_simple() and fix coding style a bit
more.