This patch enables math expression evaluation for most of the text input
controls in pcbnew.
NEW: pcbnew text input controls are able to evaluate simple
mathematical expressions, including distance units (e.g. 5.0+(2*1.2mm)).
* Add code to allow each editing window it's own undo/redo count.
* Add code to allow for infinite undo/redo when count is set to 0.
* Add edit control to all editing windows general options dialog for
user configuration of undo/redo count.
* Add code to save and restore undo/redo count for each editing window.
These settings are now not common to the board editor, because the footprint editor can be run outside the board editor.
download_boost.cmake: ignore .htm* files when installing boost. They are not used, and often have a very very long (and stupid) name which sometimes creates issues.