Check for basedir and baseurl

If these configuration values are not set php will throw an unnecessary
NOTICE.
Merge remote-tracking branch 'splitbrain/master'
rfc2231 compatible encoding for header()

This is only used in the filename header field and ensures correct
interpretation of an encoded filename. This is will be needed
especially for download of files with umlauts with an Internet Explorer.
Merge branch 'master' of https://github.com/splitbrain/dokuwiki
Merge remote-tracking branch 'splitbrain/master'
Merge pull request #845 from gamma/master

rfc2231 compatible encoding for header()