doc: Use @: where needed

doc: Use @: where needed

When an abbreviation ends with a dot followed by whitespace, Texinfo
thinks the dot ends a sentence, and applies spacing rules etc. based
on that.  To prevent this, there is the @: macro.

This patch puts @: after every vs., e.g., and i.e. where it is needed.
In a few cases there was "@ " already, or "@\n", but @: is slightly
better, and more consistent.

	* target.def: Put @: after every vs., e.g., and i.e. where it is
	followed by whitespace.
	* doc/extend.texi: Ditto.
	* doc/fragments.texi: Ditto.
	* doc/gimple.texi: Ditto.
	* doc/implement-c.texi: Ditto.
	* doc/install.texi: Ditto.
	* doc/invoke.texi: Ditto.
	* doc/md.texi: Ditto.
	* doc/plugins.texi: Ditto.
	* doc/rtl.texi: Ditto.
	* doc/sourcebuild.texi: Ditto.
	* doc/tm.texi.in: Ditto.
	* doc/ux.texi: Ditto.
	* doc/tm.texi: Regenerate.

From-SVN: r265882