Merge from trunk.

[SVN r40260]

build/Jamfile.v2

@@ -12,6 +12,9 @@ project boost/python
   : source-location ../src
   ;
 
+rule cond ( test ? : yes * : no * ) { if $(test) { return $(yes) ; } else { return $(no) ; } }
+rule unless ( test ? : yes * : no * ) { if ! $(test) { return $(yes) ; } else { return $(no) ; } }
+
 lib boost_python
     : # sources
     numeric.cpp
@@ -60,7 +63,12 @@ lib boost_python
         # python_for_extensions is a target defined by Boost.Build to
         # provide the Python include paths, and on Windows, the Python
         # import library, as usage requirements.
-        <library>/python//python_for_extensions
+        [ cond [ python.configured ] : <library>/python//python_for_extensions ]
+        
+        # we prevent building when there is no python available
+        # as it's not possible anyway, and to cause dependents to
+        # fail to build
+        [ unless [ python.configured ] : <build>no ]
       
     :   # default build
         <link>shared

test/Jamfile.v2

@@ -2,12 +2,20 @@
 # Software License, Version 1.0. (See accompanying
 # file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 
+import python ;
+
 use-project /boost/python : ../build ;
 project /boost/python/test ;
 
+local PY = ;
+if [ python.configured ]
+{
+  PY = /python//python ;
+}
+
 rule py-run ( sources * : input-file ? )
 {
-    return [ run $(sources) /boost/python//boost_python /python//python
+    return [ run $(sources) /boost/python//boost_python $(PY)
       : # args
       : $(input-file)
       : #requirements
@@ -39,7 +47,7 @@ test-suite python
   :
 
   [
-    run exec.cpp ../build//boost_python/<link>static /python//python
+    run exec.cpp ../build//boost_python/<link>static $(PY)
       : # program args
       : exec.py
       : # requirements
@@ -183,7 +191,7 @@ bpl-test crossmod_opaque
   :   
   :
   : <define>BOOST_PYTHON_STATIC_LIB
-    <use>/python//python
+    <use>$(PY)
 
 ]