Improvements to scons build for beast.

* Common code extracted to Python directories.
* Read ~/.scons file for scons environment defaults.
* Override scons settings with shell environment variables.
* New "tags" for debug, nodebug, optimize, nooptimize builds.
* Universal platform detection.
* Default value of environment variables set through prefix dictionaries.
* Check for correct Boost value and fail otherwise.
* Extract git describe --tags into a preprocesor variable, -DTIP_BRANCH
* More colors - blue for unchanged defaults, green for changed defaults, red for error.
* Contain unit tests for non-obvious stuff.
* Check to see that boost libraries have been built.
* Right now, we accept both .dylib and .a versions but it'd be easy to enforce .a only.

python/beast/util/Tests.py

@@ -0,0 +1,31 @@
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+import os
+
+from beast.util import File
+
+LIBS_PREFIX = '// LIBS:'
+MODS_PREFIX = '// MODULES:'
+
+def build_executable(env, path, main_program_file):
+    """Build a stand alone executable that runs
+       all the test suites in one source file."""
+    libs = File.first_fields_after_prefix(path, LIBS_PREFIX)
+    source_modules = File.first_fields_after_prefix(path, MODS_PREFIX)
+    source_modules = File.sibling_files(path, source_modules)
+
+    bin = os.path.basename(os.path.splitext(path)[0])
+    bin = os.path.join('bin', bin)
+
+    # All paths get normalized here, so we can use posix
+    # forward slashes for everything including on Windows
+    srcs = File.child_files('bin', [main_program_file, path] + source_modules)
+    objs = [File.replace_extension(f, '.o') for f in srcs]
+    if libs:
+        env.Append(LIBS=libs)  # DANGER: will append the file over and over.
+    env.Program(bin, srcs)
+
+def run_tests(env, main_program_file, root, suffix):
+    root = os.path.normpath(root)
+    for path in File.find_files_with_suffix(root, suffix):
+        build_executable(env, path, main_program_file)