Reorganized the contents of the sipsimple.util module

Ignore-this: 6bbbf6bf13b7bee9eea2bee24c37e52c

darcs-hash:20100111113858-1e3d8-e72c25c5d0fd5c13ba01b7500c86e818998a11b0
Fixed signature of GenericException._get_message

Ignore-this: 143f62758f790a688567b28531a2afd9

darcs-hash:20100111115235-1e3d8-6edd6557735d28a288a7724721f33467f3b9e00e