give load()/include() with target and infile()/$$fromfile() a clean environment

load()/include() with a target namespace would inherit the current
context. however, if you source a project with all bells and whistles,
this makes completely no sense and may be actually counterproductive.

infile()/$$fromfile() would have interited only the functions from the
current context. that was only a hack to support abusing them.

Change-Id: I2e992b923d9e5b0e5056001ca49b35de573abc63
Reviewed-by: Joerg Bornemann <joerg.bornemann@nokia.com>

dist/changes-5.0.0

@@ -203,6 +203,8 @@ information about a particular change.
 - qmake
   * Projects which explicitly set an empty TARGET are considered broken now.
   * The makespec and .qmake.cache do not see build pass specific variables any more.
+  * load()/include() with a target namespace and infile()/$$fromfile() now start with
+    an entirely pristine context.
   * Configure's -sysroot and -hostprefix are now handled slightly differently.
     The QT_INSTALL_... properties are now automatically prefixed with the sysroot;
     the raw values are available as QT_RAW_INSTALL_... and the sysroot as QT_SYSROOT.

qmake/project.cpp

@@ -1633,7 +1633,7 @@ QMakeProject::doProjectInclude(QString file, uchar flags, QHash<QString, QString
         if(flags & (IncludeFlagNewProject|IncludeFlagNewParser)) {
             // The "project's variables" are used in other places (eg. export()) so it's not
             // possible to use "place" everywhere. Instead just set variables and grab them later
-            QMakeProject proj(this, &place);
+            QMakeProject proj(prop);
             if(flags & IncludeFlagNewParser) {
                 parsed = proj.read(file, proj.variables()); // parse just that file (fromfile, infile)
             } else {