OpenXML: Strip w:lastRenderedPageBreak when merging runs

[Chase Tingley]

Word computes page break locations and caches their locations as a <w:lastRenderedPageBreak/> element. Like spelling mistakes, this is a computed value that Word will generate on its own. (Additionally, the cached value is probably invalid in translation, due to changing text lengths.)

We should strip it when merging text runs.

[Chase Tingley]

Fix Issue #478 - strip w:lastRenderedPageBreak from docx files

→ <<cset c9f6d38fcf7b>>