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/String_test.py

@@ -0,0 +1,36 @@
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+from unittest import TestCase
+
+from beast.util import String
+from beast.util import Terminal
+
+Terminal.CAN_CHANGE_COLOR = False
+
+class String_test(TestCase):
+  def test_comments(self):
+    self.assertEqual(String.remove_comment(''), '')
+    self.assertEqual(String.remove_comment('#'), '')
+    self.assertEqual(String.remove_comment('# a comment'), '')
+    self.assertEqual(String.remove_comment('hello # a comment'), 'hello ')
+    self.assertEqual(String.remove_comment(
+      r'hello \# not a comment # a comment'),
+      'hello # not a comment ')
+
+  def test_remove_quotes(self):
+    errors = []
+    self.assertEqual(String.remove_quotes('hello', print=errors.append),
+                     'hello')
+    self.assertEqual(String.remove_quotes('"hello"', print=errors.append),
+                     'hello')
+    self.assertEqual(String.remove_quotes('hello"', print=errors.append),
+                     'hello"')
+    self.assertEqual(errors, [])
+
+  def test_remove_quotes_error(self):
+    errors = []
+    self.assertEqual(String.remove_quotes('"hello', print=errors.append),
+                     'hello')
+    self.assertEqual(errors,
+                     ['WARNING: line started with " but didn\'t end with one:',
+                      '"hello'])