Pcbnew: fix Bug #1391561 (PCBNew segfaults on BOM creation).  Does not happen on all platforms. Could be due to use of data just previoulsy deleted.
Very minor other changes.

pcbnew: Modules can be selected with block selection tool without including texts & references (GAL).

pcbnew: Allows selecting module edges in module editor, when they are covered with other items (GAL).

pcbnew: Fix persistent multiple items selection box that stays after selecting a polygon/line (GAL).

Minor doc update.

Apply patch from Cirilo Bernardo with some minor changes: mainly allows also the solder mask layer and keep ref and value fields on the silk layer.

* Fix assertions in Eeschema when editing net labels, electronic rules check,
  and plotting.
* Fix assertion when opening PCB calculator.
* Fix assertions in Pcbnew when changing footprints in footprint properties
  dialog and adding or editing text.

Polyline.h: remove useless class CRect. Use the more powerful EDA_RECT instead. Clean and remove duplicate code.

- Remove a local patch that was added to trunk as wxwidgets-3.0.0_macosx_scrolledwindow.patch

An ugly if-condition replaced with a CACHE'd cmake variable.

* Patch was taken from https://trac.macports.org/ticket/44524 for the upstream
  bug of http://trac.wxwidgets.org/ticket/16329.

Fix many doxygen warnings (due to missing info, old comments, typo ...) when building the doxygen doc.

Add check for correct wxGTK version report by wx-config. If incorrect cmake fails. Compare https://bugzilla.redhat.com/show_bug.cgi?id=1077718