[bp/r48894][FIX] webdav: The test being done in prefs/php.php for the php-libxml extension was actually testing for a php-dom object class, which is a separate, but dependent library from libxml. Extensions can (and should) be tested using an 'extensions' block in the pref so now feature_webdav checks directly for libxml and bigbluebutton_feature checks for dom - and the "fake pref" file php.php will be removed in trunk later.
N.B. The class DOMDocument is actually used untested 100s of places in Tiki so should be added to tiki-check (thanks marclaporte) 
[bp/r48896][FIX] check: Add separate test for the php-dom extension - probably should be counted as ugly if not present? 


git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/11.x@48897 b456876b-0849-0410-b77d-98878d47e9d5