small helpfile fixes

lrshift minor bug fix (takes float scalars as signals)
pd~ bug fix -- hung with -ninsig 0
abs~ bug fix -- it was just badly wrong

Protection against closing dirty abstractions
closing and quitting doesn't query if everyone is clean
(but "pd perf" message turns that protection back on for performances)
ctrl-1, etc, automatically place new object under a selected one and
connect to it
return when editing an object (not a message or comment) deactivates text

multiple selection.  Fixed 2-pixel growth problem on Mac.
Made a "version" message so Pd can detect future file formats
if they ever appear.