Revert "Merge branch 'better-heredoc-support'"

This reverts commit 94bc53ee81c6e795360aa19511f4d16b922a840d, reversing
changes made to 846c71d36bc82f2829fde0ed6bbd9780ef765dd0.

I made an error when incorporating the heredoc-related code from
pi-php-mode that causes most syntax highlighting to break.  This
reverts all of that code until I do a better job of debugging the
cause of the problem.

Github-issue: 56
Update php-mode-modified after reverting the heredoc changes