Further fixes and TI Calypso Engineering Mode

[andrzej zaborowski]

Hi,
  I committed some fixes that may be useful, to the git tree at
http://folks.o-hand.com/andrew/gsmd.git to account for some issues
found by Thomas Wood when hacking openmoko-dialer2:

id 56535ca5e8d1798232c33fee5b377b2cbd2cda49 adds keeping track of
current registration state internally in gsmd. Without this the
"gsmd->dev_state.registered" variable had bogus values.

id 2348a36aab65548915c098866ce6584d564d9a47 avoids reissuing the
network initialisation commands (the ones that are issued after we
successfully register) excessively everytime the registration state
changes, for example when we merely moved to a different cell. Some
unrelated miscellaneous fixes too.

id 969ef13d8850eae854af9ea4c9a228c226741db2 tries harder to make sure
that incoming calls are rejected when the dialer requests this. I
don't know if this change is enough. Thomas has hit this issue
yesterday.

Unrelated to this, I added some information about some additional
proprietary commands that TI Calypso seems to support to the
http://wiki.openmoko.org/wiki/GTA01_gsm_modem page. Among them there's
%EM (engineering mode) which lets you do some pretty cool things with
the modem, for example tells you what other cells are in range
(besides your currently serving cell), their IDs and the strength of
signal coming from each of them. IIRC there was some discussion about
this capability earlier on this list, and there was an idea to use
this information (if available) for making a global map of cell IDs
for easy geolocation.

Cheers,
Andrew