[Dev] PARCELDIR replaced by PARCELPATH

[Morgen Sagen]

In the past you were able to set the PARCELDIR environment variable to 
specify a single directory that Chandler would look at for 'external' 
parcels (i.e., those outside of chandler/parcels).  I just replaced 
this with PARCELPATH which now takes a list of directories separated by 
a platform-specific character (':' on Mac/Unix, ';' on Windows I 
think).

~morgen