Skip downloading a potentially huge calendar file if it the same as out
local copy, using the If-Modified-Since-HTTP-Header.
Signed-off-by: Andrew McMillan <andrew@morphoss.com>
The PostgreSQL database returns a string like "2013-01-11
18:37:36.737665+01", while curl returns the file-modification-time as a
string repesenting the secondes since the UNIX epoche. Comparing them as
strings us wrong.
Convert them to DateTime() instances instead.
And only do this when the filetime is actually returned.
Signed-off-by: Andrew McMillan <andrew@morphoss.com>
