Fix for bug 1258, manual tax on invoice screen did not respect number formats

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extra : source : e5310245cde61ea4645b3643dc180a2d626399d9
Amending changelog for 1.3-only fix

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extra : source : 234388d09430302c3d9ae11ec51caa272262d4b3
Merge pull request #477 from einhverfr/1.4

including fix for 1258