Use @pxref when necessary

Use @pxref when necessary

* doc/lispref/customize.texi (Composite Types):
* doc/lispref/edebug.texi (Specification List):
* doc/lispref/variables.texi (Local Variables):
* doc/misc/efaq.texi (Basic keys):
(Informational files for Emacs):
* doc/misc/flymake.texi (Locating a master file):
* doc/misc/gnus.texi (Don't Panic):
(Oort Gnus):
* doc/misc/htmlfontify.texi (Non-interactive):
* doc/misc/mh-e.texi (More About MH-E):
* doc/misc/pcl-cvs.texi (Entering PCL-CVS):
* doc/misc/tramp.texi (Remote processes):
* doc/misc/vhdl-mode.texi (Indentation Calculation):
(Custom Indentation Functions): Use @pxref when inside parens.