Fix some coverity warnings (not initialized members). Add comments. Better (more informative) title in dialog to download .pretty libs.

Fix someminor  coverity warning, and one bug found by coverity in drill report files : buried holes were not properly counted and listed.

lib_dxf: Update to version 0.5.13 (previous: 0.5.11) due to a bug (memory leak) fixed in 0.5.13, which has also more comments, and try to fix most of coverity warnings (not initialized class members).
These members are now initialized, which also fix some other more serious coverity issues.

pcbnew, place file: Fix a minor bug in side identification: a comment in file header was generated with always "top side" id even when the bottom side file was created. Fix also a minor coverity warning (no bug)

Pcbnew, Footprint place file: use standard keywords "top" and "bottom" as board side identifiers instead of external copper layers names, which have no meaning in this fabrication file

Move exact dialog: make all messages translatable. Fix minor issues (some can be Windows specific). Remove useless declarations. Fix coding style issues
Fix minor warnings from cppcheck.

Fix also very minor warnings detected by cppcheck.

* move not shared files (sch_item_struct.*, sch_base_frame.h) to eeschema;
* move wxEeschemaStruct.h to eeschema and rename it schframe.h to be consistent with the other corresponding file name schframe.cpp;
* remove few not needed  #include

Pcbnew: fix bug  #142348 (airwire does not always appear after deleting a track). Very minor other fixes.

* Fix coverity scan error for array comparison.
* Check for buffer length overflow that fixes segfault.

* Add support for setting python site package path to PYTHON_SITE_PACKAGE_PATH.
* Move configure_file() so WXPYTHON_VERSION is already initialized before creating
  config.h (Duh!).
* Add status message to indicate the version of wxPython found.

Temporary fix a crash I created in rev 5427, when erasing all modules on a board and read the netlist. Will be fully fixed later.
Very minor fixes: remove duplicate #define in vrml_v2_modelparser.cpp, and "undo" a very minor change I made in class_board.cpp when I tried to fix a Pcbnew crash.

Pcbnew: fix  Bug #1422093 (pcbnew crashes after editing a footprint cominng from the board  with the fp editor and saving it on a librray and trying to load it to the board)
Some other very minor fixes.

* Fix resource leak in idf_parser.cpp
* Fix logically dead code in idf_parser.cpp
* Fix use after free bug in idf_parser.cpp
* Fix unitialized scalar value in idf_parser.cpp
* Fix logically dead code in idf_outlines.cpp
* Fix unitialized scalar value in idf_outlines.cpp
* Fix invalid iterator in idf_common.cpp
* Fix unitialized scalar value in vrml_layer.cpp

* Fix unitialized variable in MSG_PANEL_ITEM default ctor.
* Fix a bunch of uncaught exception issues.
* Fix a memory leak in the NETLIST_READER::GetNetlistReader() when an
  an attempt to read an invalid net list file occurs.

* Add support for VRML DEF coordinate key word.
* Coding policy fixes by Blair Bonnett <blair.bonnett@gmail.com>
* Debugging output clean up.

This method is added for scripting purposes, to be able to query
specific board layer names thru a board object.

If no board specific layer name is found, it will fallback to
standard layer names.