Utilities: Fix absolute URL in baseurlpath.

A bug in the 'baseurlpath' parsing meant that 'https://example.org/'
was not considered a valid value for 'baseurlpath'.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@2984 44740490-163a-0410-bde0-09ae8108e29a