Log Message:
Update to 3.18.1 which makes it actually build with sip-4.8.x.

Changes in 3.18.1 since 3.18:

* Fixed the handwritten code for all QDomDocument.setContent() overloads
  which was using deprecated (and now removed) sipBuildResult() format
  characters.
* Fixed a build problem that affected Python v2.5 and earlier.

Changes in 3.18 since 3.17.6:

* Removed some compiler warning messages.
* Reverted the changes that removed the use of sipSelfWasArg in handwritten
  code.
* Tweaked configure.py so that Python3 can run just enough of it to display
  an error message.
* Fixed a regression in emitting Python signals to Qt signals.
* Handwritten code changes for the removal of the sipProtectVirt_*() methods.
* Fixed a build problem with the GPL version.
* Refactored the signla/slot support.
* Safety checking of latest signal/slot refactoring.
* Safety commit of the PyQt3-specific meta-type and super-type (just stubs
  at the moment).
* Use the %Plugin directive to enable PyQt3 signal support.
* More changes to the QObject.sender() support.
* Updated the QObject::sender() support in response to sip changes.
* Moved the last of the type parsing from sip.
* The type parsing now uses sipResolveTypedef().
* Added the type parsing support from the sip module as PyQt4 no longer uses
  it.
* Replaced sipFindConnection() with sipFindSlot().
* Replaced sipFreeConnection() with sipFreeSipslot().
* Changes required by recent changes to the Qt support API.
* Compatibility changes needed for SIP v4.8.
* Merged the v3.17 maintenance branch into the trunk.
* Made some char* in handwritten code const needed by SIP v4.8.