- re-worked PNS_LINE_PLACER and PNS_ROUTER classes a bit, removing duplicate class members
- cleaned up Andrew's blind/buried via fixes
- fixed 'custom via width' dialog bug updating the width even when closed/cancelled
- fixed incorrect radius of drawn microvias

2) Change from legacy Cu stack to counting down from top=(F_Cu or 0).
   The old Cu stack required knowing the count of Cu layers to make
   sense of the layer number when converting to many exported file types.
   The new Cu stack is more commonly used, although ours still gives
   B_Cu a fixed number.
3) Introduce class LSET and enum LAYER_ID.
4) Change *.kicad_pcb file format version to 4 from 3.
5) Change fixed names Inner1_Cu-Inner14_Cu to In1_Cu-In30_Cu and their
   meanings are typically flipped.
6) Moved the #define LAYER_N_* stuff into legacy_plugin.cpp where they
   can die a quiet death, and switch to enum LAYER_ID symbols throughout.
7) Removed the LEGACY_PLUGIN::Save() and FootprintSave() functions.
   You will need to convert to the format immediately, *.kicad_pcb and
   *.kicad_mod (=pretty) since legacy format was never going to know
   about 32 Cu layers and additional technical layers and the reversed Cu
   stack.

Pcbnew: fix a minor bug: in zones with no net, only the zone clerance was used to created clearence,  regardless the pad or footprint local clerance.
Very minor other fixes.

Fixes the bug that causes pcbnew crash, when there are multiple net classes and the plot dialog was opened.
Changed NETCLASS* to boost::shared_ptr<NETCLASS>.

Most of the changes are just adding GetDesignSettings() before every occurence of m_NetClasses.
More complex changes:
class_netclass.cpp - NETCLASS does not store the pointer to the parent BOARD anymore. Added function SetParams( BOARD_DESIGN_SETTINGS& ).
class_netclass.h - Removed GetTrackMinWidth(), GetViaMinDiameter(), GetViaMinDrill(), GetuViaMinDiameter(), GetuViaMinDrill() as they were refering to BOARD_DESIGN_SETTINGS anyway (they are not net class specific).
kicad_plugin.cpp - filters out empty nets (that are anyway not saved) when storing net class information. Previously it was done in NETCLASS::Format() function.

- SEGVIA becomes VIA
- Drill size moved from TRACK to VIA
- Removed shape from TRACK, becomes ViaType in VIA
- GetTrace becomes GetTrack, for uniformity
- Some minor constification and typo fixes

Renamed BOARD_CONNECTED_ITEM::SetNet() -> SetNetCode()
Added BOARD_CONNECTED_ITEM::GetNet() for accessing NETINFO_ITEM* of a given item.
Fixed module editor crash when launched to edit a module from a PCB.
Replaced some BOARD::FindNet( item->GetNet() ) calls with BOARD_CONNECTED_ITEM::GetNet().

Renamed BOARD_CONNECTED_ITEM::SetNet() -> SetNetCode()
Added BOARD_CONNECTED_ITEM::GetNet() for accessing NETINFO_ITEM* of a given item.
Fixed module editor crash when launched to edit a module from a PCB.
Replaced some BOARD::FindNet( item->GetNet() ) calls with BOARD_CONNECTED_ITEM::GetNet().

Undo buffer for the PNS router. Still, it has a bug - it crashes when an undo/redo operation is performed while routing a track.

RN_DATA::Update()/AddSimple() take BOARD_ITEM* as the parameter (instead of being split to versions with BOARD_CONNECTED_ITEM* and MODULE*), to make the code look clearer.

Fixed Push and Shove and ratsnest cooperation (tracks added by PNS are taken into account while calculating ratsnest).