Minor fixes and enhancements.

* Add general purpose user write permission test function to base
  window class.
* Check user write permissions before saving project, schematic and
  library files.
* Remove displaying file dialog every time the project file is saved.
* Display absolute paths for non-root sheet file in title bar.
* Remove redundant command table entry from schematic editor.
* Remove unused variables to fix GCC 4.6 warnings.
* The usual Doxygen comment and coding style policy fixes.

* Disable save library command when user does not have permission to write
  the active library.
* Append the active library file name displayed in the title bar with read
  only when the user does not have write permission.
* Test the selected folder permissions when user chooses the save library
  as command.
* The obligatory coding style policy fixes.

zone to zone DRC 'clearance' policy/setting now comes from ZONE_CONTAINER::GetClearance(), a virtual override, and is currently ignoring the netclass setting and using only the m_ZoneClearance settting, see ZONE_CONTAINER::GetClearance() to adjust policy.

pcbnew's footprint editor was not injecting the m_LocalClearance setting back into an existing board after a module edit

Store the name of modedit active(/current/working?) library in a static variable. Edit some modedit strings.

Pcb calculator: add track width versus current and electrical spacing versus voltage tools (from IPC 2221)

Eeschema: optimize import of footprints names ( .stf files) that was time consumming with large designs.

Eeschema: optimize import of footprints names ( .stf files) that was time consumming with large designs.

* Fix 3D frame issue (3D frame not show) when it is iconized and reactivated by Pcbnew or CvPcb menus (Windows only)
* Add in help menu a direct link to the new doc Getting_Started_in_KiCad.pdf, written by contributors (useful for beginners)
* Fix other very minor issues in CvPcb.
* Update howto doc about translation

* Raise 3D frame in PCB editor and module editor instead of displaying a message
  dialog indicating that the 3D viewer is already open.
* Raise 3D viewer and module viewer in CVPCB to mimic the behavior changed in
  PCBNew.
* Set focus to OpenGL canvas when creating 3D viewer so mouse wheel events
  are handled on Windows without having to click on the canvas.
* Rename 3D viewer frame class from WinEDA3D_DrawFrame to EDA_3D_FRAME.
* The usual smattering of coding policy fixes.

* Move clarification menu icon code from base board item object to the appropriate
  object.
* Remove left over French comments.
* Coding policy fixes.

Pcbnew: Fix bug 811437 . This bug (due to duplicate time stamps), cannot happen with usual boards, only when 2 identical board (from the same .brd file) are append.

* Move menu text code from base board item object to the appropriate
  object.
* Add helper to get board layer to base board item object.

eeschema: add SCH_SHEET_PIN_T in ParentItems collector, convert sch_collectors.* to native unix format

Eeschema: fix bug that crashes libedit (after creating a new pin, repeat it (insert key), delete the new repeated pin and try to repeat)

Pcbnew: fix bug in D_PAD ctor: m_LengthDie not initialized. Disable m_LengthDie read from .brd files,
because this bug breaks compatibility with older version of Pcbnew , and the stored value as most of time no sense.
To enable m_LengthDie reading, see class_pad.cpp

All: use double instead of int to store zoom values.