(Bug 52430) Accept more non-standard WS in xmlish tags

* Added a parser test for <ref> tags, but this fix applies to
  <*include*> tags as well. Since we don't try to preserve the
  non-standard whitespace, the new test is wt2html only.

Change-Id: I2690f066749cf3b3cfcfc4a64ffbd3dd41ff5ec3
Merge "(Bug 52430) Accept more non-standard WS in xmlish tags"