Close #493

Patch from atmo.

SHM is autodetected, so there is not point in disabling it by force.

item-change for IM callback.
Check callback and handle other than interface-update stuff only if they
have same id than current input

Should fix that meta not showing/too many signals sended in beginning.
Shouldn't break anything (as always ;)

Patch by aballier.

This fixes opening file names with colons which some users,
at the expense of requiring "://" to separate the access from the path.
As such udp:@12.34.56.87 won't work anymore, use udp://@12.34.56.87 instead.