Fix performance regression when importing JS files.
Fix performance regression when importing JS files.

A side effect of the bugfix commit 33c9a2721b was that two imports of
the same file were no longer considered the same if the import location
differed. This results in a considerable slowdown due to more cache
misses, so restore the old behvior in this regard.
Also, JSImport's qHash() and operator==() are now consistent.

Change-Id: I23acd665a6329ec1ab132cb34657f0b05357093f
Reviewed-by: Joerg Bornemann <47777b9406dbddd02a3fdca8341789a013805a11@theqtcompany.com>

qtproject/qt-labs-qbs,qt-labs/qbs,gatzka/qt-labs-qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,gatzka/qt-labs-qbs,qt-labs/qbs,gatzka/qt-labs-qbs,gatzka/qt-labs-qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs