dev-python/ipython: Version bump + possible fix for test phase

[marbre]

@jlec @SoapGentoo

I hopefully fixed the call of run_tests() in 4.1.2 which was accidentally broken due to the EAPI bump. However, tests currently fail on my machine with

 * Call stack:
 *     ebuild.sh, line  133:  Called src_test
 *   environment, line 3837:  Called distutils-r1_src_test
 *   environment, line 1074:  Called _distutils-r1_run_foreach_impl 'python_test'
 *   environment, line  409:  Called python_foreach_impl 'distutils-r1_run_phase' 'python_test'
 *   environment, line 3330:  Called multibuild_foreach_variant '_python_multibuild_wrapper' 'distutils-r1_run_phase' 'python_test'
 *   environment, line 2421:  Called _multibuild_run '_python_multibuild_wrapper' 'distutils-r1_run_phase' 'python_test'
 *   environment, line 2419:  Called _python_multibuild_wrapper 'distutils-r1_run_phase' 'python_test'
 *   environment, line  697:  Called distutils-r1_run_phase 'python_test'
 *   environment, line 1007:  Called python_test
 *   environment, line 3716:  Called virtx 'run_tests'
 *   environment, line 4429:  Called die
 * The specific snippet of code:
 *       XHOST=$(type -p xhost) || die;

Anyway, this is the case for all ipython ebuilds currently in the tree and might be related to my machine. The EAPI=5 ebuils fail with a similar message, also additionally virtalmake is called before vitx.

Furthermore the version bump adds a new dependency (prompt_tool) to the ipython ebuild and adds a more specific dependency on traitlets.