fix shell command injection
add way to test command under windows
change command to which available under most unix systems

agree i will change it which is available under suse, ubuntu, debian, fedora, bsd
bug #11598 [Finder] Shell escape and windows support (Gordon Franke, gimler)

This PR was merged into the 2.3 branch.

Discussion
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[Finder] Shell escape and windows support

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

Add escaping of command passed to Shell::testCommand().
Fix todo add support for windows.

Commits
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c70a226 change command to which available under most unix systems
85e77b1 add way to test command under windows
4fa9288 fix shell command injection