Compiler: fix ps1_escape call to use return value
tcsh: full escaping

^, \, and \n are now supported for tcsh, as well as any other char.
At least one thing is ok in tcsh: escapes in 'prompt'. ;^)
Portability: make $PS1_fallback portable

The build of $PS1_fallback (the default prompt displayed in case of
failure of the evaluation of the dynamic prompt) now uses
AngelPS1::Shell instead of being hardcoded to bash symbols.
tcsh: full implementation of the angel controller: quit/on/off

The missing commands in the angel controller are now implemented.

The main issue of history pollution is still there and still makes
angel-PS1 unusable with tcsh.