Regression tests now run under scons!

For example, 'scons ALPHA_SE/test/opt/quick' will build
ALPHA_SE/m5.opt if necessary and run all the self-identified
"quick" tests on it.  Other possibilities:
- Run just test1: scons ALPHA_SE/test/opt/test1
- Run all tests:  scons ALPHA_SE/test/opt
- Run all tests on debug build: scons ALPHA_SE/test/debug
- Update test1 reference outputs in m5-test:
scons update_ref=y ALPHA_SE/test/opt/test1
The proper tests will be selected based on the setting
of FULL_SYSTEM, ALPHA_TLASER, etc.

README:
    Update directions to use scons-based test invocation.
SConscript:
    Return list of generated build environments to SConstruct
    so it can associate tests with each of them.
    Set 'M5Binary' attribute on each env to record name of
    generated binary to be tested.
build/SConstruct:
    - Support invoking m5-test tests via scons.
    - Add new non-sticky option category, for 'update_ref'.
    - Move existing "sticky" option definitions out of
    build_dir loop.  Someday we can generate help text
    from these.
    - Make 'CC' and 'CXX' sticky options; use environment vars as
    defaults if available.
    - Make config builder more scons-y.
python/m5/__init__.py:
    Make AddToPath() correctly handle relative path arguments.
    Assumes that sys.path[0] has the directory where the current
    Python file lives; new m5execfile() function sets this up
    properly for exec'd files.

--HG--
extra : convert_revision : 48896688592e210d8e63f96c34e57474853d0e66

python/m5/__init__.py

@@ -31,12 +31,25 @@ def panic(string):
     print >>sys.stderr, 'panic:', string
     sys.exit(1)
 
-# Add given directory to system module search path, if it is not
-# already there.
+def m5execfile(f, global_dict):
+    # copy current sys.path
+    oldpath = sys.path[:]
+    # push file's directory onto front of path
+    sys.path.insert(0, os.path.abspath(os.path.dirname(f)))
+    execfile(f, global_dict)
+    # restore original path
+    sys.path = oldpath
+
+# Prepend given directory to system module search path.
 def AddToPath(path):
+    # if it's a relative path and we know what directory the current
+    # python script is in, make the path relative to that directory.
+    if not os.path.isabs(path) and sys.path[0]:
+        path = os.path.join(sys.path[0], path)
     path = os.path.realpath(path)
-    if os.path.isdir(path) and path not in sys.path:
-        sys.path.append(path)
+    # sys.path[0] should always refer to the current script's directory,
+    # so place the new dir right after that.
+    sys.path.insert(1, path)
 
 # find the m5 compile options: must be specified as a dict in
 # __main__.m5_build_env.