FindPython: Add IronPython support on all platforms

Modules/FindPython2.cmake

@@ -118,6 +118,8 @@ This module will set the following variables in your project
 ``Python2_COMPILER_ID``
   A short string unique to the compiler. Possible values include:
     * IronPython
+``Python2_DOTNET_LAUNCHER``
+  The ``.Net`` interpreter. Only used by ``IronPython`` implementation.
 ``Python2_Development_FOUND``
   System has the Python 2 development artifacts.
 ``Python2_Development.Module_FOUND``
@@ -235,7 +237,10 @@ Hints
     ``RPython translation toolchain`` to produce the python interpreter.
     See `PyPy <https://www.pypy.org>`_.
 
-  The default value is the list: ``CPython``, ``IronPython``.
+  The default value is:
+
+  * Windows platform: ``CPython``, ``IronPython``
+  * Other platforms: ``CPython``
 
   .. note::
 
@@ -245,6 +250,12 @@ Hints
     ``Python2_FIND_STRATEGY=LOCATION``, each location will be search first for
     ``IronPython`` and second for ``CPython``.
 
+  .. note::
+
+    When ``IronPython`` is specified, on platforms other than ``Windows``, the
+    ``.Net`` interpreter (i.e. ``mono`` command) is expected to be available
+    through the ``PATH`` variable.
+
 Artifacts Specification
 ^^^^^^^^^^^^^^^^^^^^^^^
 
@@ -257,6 +268,9 @@ setting the following variables:
 ``Python2_COMPILER``
   The path to the compiler.
 
+``Python2_DOTNET_LAUNCHER``
+  The ``.Net`` interpreter. Only used by ``IronPython`` implementation.
+
 ``Python2_LIBRARY``
   The path to the library. It will be used to compute the
   variables ``Python2_LIBRARIES``, ``Python2_LIBRAY_DIRS`` and