Allow for possibility that drupal folder resides outside of the civicrm folder

Per Tim's suggestion moving the drupal module to the same level folder as the top level core folder would make code management easier (especially when working with more than one CMS version). Tim's suggested structure was

civicrm
– drupal
– packages
– civicrm-core

(potentially tools at that level too.)

I had a look at this & in the context of drupal 7 I seemed to be able to achieve this by altering a few drupal 7 specific code locations. I'm not concerned at this stage with any of the folders other than the drupal folder. One question is whether the civicrm code base folder should be civicrm-core or just core (I favour the former simply because it matches the github repo - but should possibly rename 'drupal' to civicrm-drupal' in that case - which also seems to make sense)

http://forum.civicrm.org/index.php/topic,30003.msg128748.html#msg128748