InspIRCd: various formula improvements.

* Use the main website domain instead of the GitHub one.
* Remove the explicit head branch specification as this is now the
  default.
* Fix a typo in one of the module file names.
* Depend on the postgresql formula as it is not part of the system
  on Mavericks.

Closes #24535.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>