Work around Windows limitation in createTemporaryDirectory()

Windows really does not let you delete files that are in use, even if
"in use" really means that there is a ClassLoader referencing that file
and that ClassLoader just happens not to be garbage-collected yet.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Ensure createTemporaryDirectory() can be called in a loop

When calling said method from the same code location multiple times, we
should still get an empty temporary directory every time, even if there
are still-open files in the directory of the default name. For Windows,
emptying directories poses an insurmountable problem when they contain
files that are still in use, therefore we have to fall back to creating
new temporary directories.

Identified by Jennyver Jenkins as a problem when building and testing
ij1-patcher on Windows.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge pull request #72 from scijava/windows-temp-dir

Work around Windows problems with temporary directories