Use prepareTextForEdit or prepareContentForEdit

Avoid content reparse during NewRevisionFromEditComplete by fetching
ParserOutput either from prepareTextForEdit or prepareContentForEdit.

https://gerrit.wikimedia.org/r/#/c/95519/
https://gerrit.wikimedia.org/r/#/c/95530/
Merge pull request #24 from SemanticMediaWiki/page-editinfo

Use prepareTextForEdit or prepareContentForEdit