variables markers: allowing x-* markers

[Dwayne Bailey]

You can currently only use markers defined in Gettext itself such as
c-format and no-c-format.  It would be useful in cases where PO is being
used outside of the normal Gettext domain to allow user defined markers
such as x-oo-format.  This simple addition would allow Gettext to
operate normally and other tools that can manipulate these files to be
able to execute valid operations based on the information.

-- 
Dwayne Bailey
Translate.org.za

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