by default read from lib/commands/default.def
A .def file allows to define a command with
\define "Name" "lfun"
where Name is the name of the new command and lfun is the code
to be executed.
\def_file "FileName"
allows to include another .def file.
The implementation of CmdDef is similar to KeyMap, i.e. there is
one instance created in the LyX.cpp that reads the .def file, holds
a list containing all definitions, and supplies access methods.
LFUN_CALL: The new lfun is used to execute a command definition, e.g.
call Name
If a toolbar item has the associated action "call Name" then the image
lib/images/commands/Name.png is used for the button.
git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@21093 a592a061-630c-0410-9148-cb99ea01b6c8