filter-branch: Grok special characters in tag names

filter-branch: Grok special characters in tag names

The tag rewriting code used a 'sed' expression to substitute the new tag
name into the corresponding field of the annotated tag object. But this is
problematic if the tag name contains special characters. In particular,
if the tag name contained a slash, then the 'sed' expression had a syntax
error. We now protect against this by using 'printf' to assemble the
tag header.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>