contrib: handle @option as indicating command to @table

Add support for '@table @option'.  We already support '@option{text}',
this just ensures that @option as the indicating command for table is
handled the same way.

The binutils-gdb project uses a slightly modified version of this
script to build its own man pages, this is my attempt to ensure fixes
flow back to the gcc project.  I checked the gcc docs and '@table
@option' is not currently used, so this change will make no difference
for gcc.

contrib/ChangeLog:

	* texi2pod.pl: Handle @option as indicating command to @table.