Check that root is a valid file path and if it isn't regenerate the less cache.
Check that root is a valid file path and if it isn't regenerate the less cache.

Fixes issues when copying the cache file between servers, IE when copying the uploads dir from live to local.

Fixes #5

sanchothefat/wp-less,danielhomer/wp-less,scottsweb/wp-less,Tarendai/wp-less,phongmedia/wp-less,lkraav/wp-less