Fix parsing of rrdfiles containing escapes

This fixes parsing of URLs such as 'rrd.php?path=some%3Ffile.rrd', and
if people really insist, paths such as 'C:\bar.rrd' (must be written as
'C\:\\bar.rrd', add additional escapes for Javascript strings if needed).
Merge pull request #17 from Lekensteyn/fixes

Fix parsing of rrdfiles containing escapes