Adding dependencies for MinGW/MSYS build of OpenSSH.
Removing Cygwin build of OpenSSH, because now wer're using
a MinGW/MSYS build instead.
Switching from Cygwin build of OpenSSH to MSYS/MinGW.
UpperCamelCase class methods, as used in wxPython.
Removing CYGWIN references, and ensuring that connected and
disconnected icons are only loaded once from disk.
Don't need to check private key permissions, now that we are using
the MinGW/MSYS build of OpenSSH.  We could add some checks using
"icacls.exe", but trying to map Windows permissions to POSIX
permissions (as done by Cygwin builds of OpenSSH) is not always
reliable.
Fixed module, function name and line number rendering in log format
strings, renamed a few things (using UpperCamelCase for class methods
and lowerCamelCase for variables, as commonly done in wxPython), and
started preparing for implementing the Submit Debug Dialog.
When resuming a staging upload, there is no need to recalculate the MD5
sum (which is time-consuming for large files) if it is already available
in the datafile record.  The upload stuff still needs to be moved into a
model class.
Improving message displayed when canceling uploads.
Canceling will now try to terminate any existing SCP processes.
Switched from Cygwin to MSYS, meaning that checking private key
permissions is no longer necessary (and it doesn't make sense to
map Windows permissions to POSIX permissions anyway).  Now supporting
chunked SCP uploads for large files, whole-file SCP uploads for small
files and chunked "cat >>" for small files (which is better than
whole-file SCP for updating progress bars).  MyData attempts to resume
partial uploads, but more testing of this functionality is needed, e.g.
we need to ensure that the previously uploaded file size is a whole
number of chunks.