Added GUI portion of dialog for getting a new CADC certificate.
Merge branch 'master' into retries
Added function for downloading a new CADC certificate given the 
username and password.
Added VOSpaceErrorHandler class which is used by the download 
manager.  Using this the application can now gracefully handle 
CADC certificate problems.
Set focus on username field in certificate dialog so that the user doesn't 
have to click anywhere before entering their credentials.  Made the
get certificate button default so that it is triggered on pressing enter.
Added basic test case for VOSpaceErrorHandler.
Merge branch 'master' into retries
Added profiling directory to gitignore.
Removed unnecessary call to redraw in the matplotlib image viewer's
method for refreshing the image colormap.  Profiling while tabbing 
showed the CPU time spent in the refresh colormap method dropped
from about 30% to about 3%.
Added optional redraw parameter to view_image and draw_circle.
This allows us to only redraw the figure once when moving to look at a 
new image with circle draw on it.
Profiling showed that as a result the time spent in the view_image
method when tabbing was reduced from about 40% to about 10%.
Moved MPCWriter import to the function where it is used so that the 
mpc module does not get loaded unless it is needed (i.e. we are in the
reals task).  This is in an effort to reduce startup time.  mpc adds a 
significant overhead due to the fact that it import astropy modules for 
formatting ra and dec.
Moved daophot import to the method where it is used so that IRAF is not
loaded unless needed.  This improves startup time for processing 
candidates.
Force iraf load up front in process reals task to avoid lag when accepting
first source.
Merge pull request #88 from drusk/optimize_tabbing

Closes #86.
Merge pull request #87 from drusk/cert_error_handling

Closes #49.
Merge pull request #90 from drusk/optimize_startup

Closes #89.