Portability fix for calculating package SHA sums

Use Digest::SHA1 from the standard library instead of shelling
out to the 'sha1sum' utility which is named shasum under OS X
Remove StlSymbolsLeopard.cpp

This commit removes support for OS X 10.5 from the updater and removes
the StlSymbolsLeopard workaround that was required with it.
Bump deployment target from OS X 10.5 to 10.6

MD-20245
test: none
Allow containing project to override the OS X deployment version

Also fix a build issue due to AuthorizationExecuteWithPriviledges
being deprecated in OS X 10.7 when setting the OS X min deployment
version to 10.7 or later.

MD-19353
test: none
Fix C++11 builder under GCC

Use decltype(T) instead of typeof(T) under C++11

MD-19353
Remove empty directories in the installation dir after update

If a directory was removed from one version of the app
to the next, all of the files inside the directory
would be removed but a hierarchy of empty directories would
be left behind.

On OS X this caused code signing checks to fail after updating
from a release which stored code signing-related files in
'Contents/_CodeSignature' for an embedded framework to
'Versions/4/_CodeSignature', since the old _CodeSignature dir
was never removed.

MD-20523
test: auto: TestFileUtils
Instead of always using the temporary file /tmp/libupdatergtk.so generates a new name.

This solves a problem: if the file already existed and the current user
couldn't truncate it the auto update couldn't use the Gtk auto-updater.

In this commit it also deletes the file and avoids creating and closing
the file and opening again.

MD-20923
Uses FileUtils::removeFile() instead of unlink()

MD-20923
Uses tabs for indentation.

MD-20923
Uses std::string

MD-20923
Simplifies creating the char*, avoids using useless std::string

MD-20923
Uses stack-allocated array.

MD-20923
Close the file descriptor in the same method that had been opened.

MD-20923
Deletes non-needed include.

MD-20923
Merge pull request #9 from cpina/MD-20923-fix_fail_ovewrite_file

Instead of always using the temporary file /tmp/libupdatergtk.so generates a unique filename.
Merge remote-tracking branch 'upstream/master'