[SUREFIRE-946] prevent hanging main process if forked process was killed (softly)
Use ShutdownHookUtils
[SUREFIRE-949] add forkCount parameter, making the inconsitent forkMode parameter deprecated.

- All defaulting works as in the previous versions, with the exception of reuseForks (introduced in the last release). It's now true by default.
- forkCount supports "C" notation as in -T of maven-core
fix test (parenthesis were missing in the computation)
Added m-c-p for 2.2.1
Fixed line endings
Added gitattributes
make test more robust by removing some assertions that depend on current system load
clean up variable naming: threadNumber becomes forkNumber
[SUREFIRE-949] update documentation with new forkCount / reuseForks options

- also make ${surefire.threadNumber} replacement undocumented, as its naming is totally misleading and might give users wrong impressions
[SUREFIRE-949] update documentation with new forkCount / reuseForks options
[SUREFIRE-956] make forkNumber unique among concurrent surefire-executions in a parallel maven build