GAL undo fails when triggered during some PNS routes

[Chris Pavlina]

This doesn't always happen, but when you start a second route off a first one in PNS, and then press Ctrl-Z while still routing, segments are "randomly" deleted and an "Incomplete undo/redo operation: some items not found" error appears.

http://misc.c4757p.com/pcbnew_bug.mp4

At the moment the dialog appears in this video, I had pressed Ctrl-Z.

Application: pcbnew
Version: (after 2015-may-25 BZR unknown)-product debug build
wxWidgets: Version 3.0.2 (debug,wchar_t,compiler with C++ ABI 1002,GCC 4.2.1,wx containers,compatible with 2.8)
Platform: Linux 4.0.4-2-ARCH x86_64, 64 bit, Little endian, wxGTK
Boost version: 1.58.0
         USE_WX_GRAPHICS_CONTEXT=OFF
         USE_WX_OVERLAY=OFF
         KICAD_SCRIPTING=ON
         KICAD_SCRIPTING_MODULES=ON
         KICAD_SCRIPTING_WXPYTHON=ON
         USE_FP_LIB_TABLE=HARD_CODED_ON
         BUILD_GITHUB_PLUGIN=ON