Document support for 'info proc' on FreeBSD.

Document support for 'info proc' on FreeBSD.

Since the 'info proc' support on FreeBSD does not use /proc, reword
the documentation for 'info proc' to not assume /proc.  This includes
renaming the node to 'Process Information' and suggesting that
additional process information can be queried via different
OS-specific interfaces.  This is also cleans up the description of
'info proc' support for core files a bit as /proc is not used for core
file support on any current platform.

gdb/ChangeLog:

	* NEWS: Document that 'info proc' now works on FreeBSD.

gdb/doc/ChangeLog:

	* gdb.texinfo (pwd): Update cross-reference for Process Information
	node and remove explicit /proc reference.
	(Native): Rename subsection from SVR4 Process Information to
	Process Information.
	(Process Information): Reword introduction to be less /proc
	centric.  Document support for "info proc" on FreeBSD.