don't unnecessarily use QFileInfo::filePath()

just directly use the filename we constructed it from.

Change-Id: Ia428a2cb4b192fea6bde62dfbf35361bcfc4b21e
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
implement simple VFS to support caching during project parsing

this tremendously speeds up loading of qt 5.1 based projects (including
qt itself) under mac os, as these look up the sdk dynamically, and use
caching to avoid doing that in every subproject.

Change-Id: I833253f81c3159056fab2ff888f293b36cc2ef56
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Doc: new Python class wizard

Updated the screen shot.

Change-Id: Ie65927bb872b37b6be78160810f97b215525c14f
Reviewed-by: Sergey Shambir <sergey.shambir.auto@gmail.com>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>
minor optimization: don't concatenate strings needlessly

Change-Id: Iddec1a818ff9f3ad8b12491100883e433e4b8246
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
cache results of feature search

looking up the same files in the same locations over and over again
is a rather significant waste. in particular, looking up the CONFIG
flags that don't correspond with features has a measurable impact on qt
creator's project loading time.

Task-number: QTCREATORBUG-9154
Change-Id: Ibae3d8b7797e706a6416a7d45c77734ab1281b51
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
update m_featureRoots less aggressively

it's not necessary to immediately re-calculate the roots after assigning
QMAKE_PLATFORM - it's sufficient to do it on-demand, so merely
invalidate them. this avoids that we re-calculate them multiple times
without ever using them in between while processing specs with
distributed platform assignments.

Change-Id: If508594764811b96a577fc81c5ded34ab0453148
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>