added spock to dependencies instead of junit
replaced all tests with spock and improved them
integrationTest mustRunAfter unitTest
fixed a failing test at Windows
upgraded groovy to 2.1.6
tweaked a series of executeClient methods of TestUtils and added startServer/shutdownServer
added new test ServerOperationFromClientSpec for detecting https://github.com/kobo/groovyserv/issues/48
made integration tests using groovyclient.sh run on platformIndependent environment improved build.gradle

the issue https://github.com/kobo/groovyserv/issues/48 occurs only where 'groovyclient' is 'groovyclient.sh'.
new testing mechanism can detect the problem.
improved groovyclient.sh to exit if invocation of groovyserver fails
made groovyserver.sh independent from groovyclient for checking the server started up
addressed a path expression problem at windows which is degraded at 3df8bd9
renamed annotaions for controll to run tests
excluded ServerOperationFromClientSpec at windows by using spock configuration file
Revert "excluded ServerOperationFromClientSpec at windows by using spock configuration file"

This reverts commit c2bc844a42f917e020801f5477ac0425a205c394.
excluded ServerOperationFromClientSpec only at windows by using @IgnoreIf
made groovyserver.bat independent from groovyclient for checking the server started up
got rid of support of -Cwithout-invoking-server option at groovyclient.rb
got rid of support of -Cwithout-invoking-server option at groovyclient(.c)
changed internal task name
improved resolving additional classifier for SNAPSHOT version so that an errors cannot occurs even if there is no git command