Fix check for subprocess.check_output.

The check for the presence of subprocess.check_output should be

    try:
        return getattr(subprocess, "check_output")(*args, **kwargs)
    except AttributeError:
        ...

but one may as well always override the definition.
Merge pull request #874 from anntzer/bugfix

Fix check for subprocess.check_output.
Added codesign mechanism to windows installer to run signtool on an installer executable, assuming the certificate is installed on the build machine
minor adjustment to the path to the binary to sign
Another instance where I tried to read a numeric registry value as a string
Use system metric for icon size. Added icon to welcome screen and search frame
Fix Holger's problem with loading .mat files - need to add an ObjectNumber measurement after loading
Display a dialog box in Windows setup if user has an inappropriate or unsupported OS for their download
Remove properties to automatically reject install based on version so that the custom code runs and pops up more informative information
issue #870 uninitialized metadata matchers are shown as such
Refresh the pipeline error status after any edit
issue #245 On mac, populate the default input folder combo box with the default input folder if there are no recent choices in the registry
Import htmldialog within on_help in order to prevent WX from loading in headless mode
Fixed crash on Mac when saving figure. Add extension on Mac to figure filename if not provided.
Prevent remote measurements from overwriting local ones if identical
RIP Windows XP x64 (sorry)
Fix #878: Tell arch both 64 and 32 bit for Mac workers
Modified index cacheing to cache the index of an image_set entry in the index dataset
Merge branch 'master' of github.com:CellProfiler/CellProfiler
issue #880 - undo model saves objects to keep + defensive programming