Provide a possibility to include a build version to Qt and QtWebkit pkg files version number

To enable minor patch release IAD deliveries of Qt and QtWebkit, the pkg file version number should incorporate a build version value in addition to current major, minor and patch values. The current solution proposal is to append the build value to patch value like this: <major version>,<minor version>,<patch version><triple digit build version>

This solution would display version numbers in installation as follows at installation time:
4.6.3 build 000 -> 4.06(3000)
4.6.3 build 005 -> 4.06(3005)
4.7.0 build 000 -> 4.07(0)
4.7.0 build 005 -> 4.07(5)

Proposed solution is to use variables QT_BUILD_VERSION and QT_WEBKIT_BUILD_VERSION that default to "000" if not otherwise defined by whoever does the patch build.