fix(addtr): Do not replace indices in TextNode's data (refs #5136)

The nodereplacestr() performed by addtr() should not replace indices in
TextNode's data, as it may corrupt valid TextNode's data from the
template line.

addtr() will now only search/replace the indices in the attributes from
the template line and not in the data.
Merge pull request #1352 from eguaj/3.2-A5136

fix(addtr): Do not replace indices in TextNode's data (closes #5136)