unit tests no longer write user defaults to disk

see method docs of writeUserDefaults in ApplicationDelegate for details
add "bugreport" folder to .gitignore
log stack trace if exception is raised during command execution
iPhone layout: fix board position view width
iPhone layout: fix initial tapping in board position list view
GoMove keeps its record of captured stones when undo is invoked
board position views display number of captured stones
use special value -1 for "board position last viewed" on user defaults upgrade

when the app is upgraded to a new version and the user defaults are updated to the
corresponding new format, the "board position last viewed" property now gets a value
that will cause the app to display the last board position of the game when it is
launched for the first time after the upgrade. this is the behaviour from before the
upgrade when there was no "board position" feature, and thus fulfills the principle
of least surprise.

before the change in this commit, the app displays board position 0 after the upgrade,
i.e. the start of the game. for the unwary user who does not yet know about the new
"board position" feature, this is a big surprise - she thinks that she has just lost her
game because she does not see any stones! then, when she tries to make the first
move, she gets another surprise: the alert that warns that future moves will be discarded.
new formula for offset calculation when placeStoneUnderFinger is false

the navigation toolbar at the bottom of the new iPhone layout takes away space that
previously was available for the offset when placeStoneUnderFinger is false; the offset
calculation is adjusted so that the result is a generally smaller offset