Description of problem:

Publican doesn't like it when a PO file uses \t in msgids for a string which is a tab in the original DocBook XML.  We should add an option to avoid encoding tab as \t, and just use tab characters.  The default will still be to encode tabs, because this is how the Gettext tools behave (eg msgmerge, msgcat).

Version-Release number of selected component (if applicable):
2.0.2-SNAPSHOT

How reproducible:
100%

Steps to Reproduce:
1. Push a POT file containing tab characters into Zanata
2. Pull a PO file from Zanata
3. Observe the representation of the tab characters in the PO's msgid and msgstr fields.
  

Additional info:

The new option (in Maven's "pull" goal) will be -Dzanata.encodeTabs, which will default to true.  If the option -Dzanata.encodeTabs=false is provided, tabs should be as-is.