Use `MANTIDPATH` environment variable if it is available

This allows for people using `mantidpython`. This change
also removes the ability to set the location of mantid from
the command line.

docs/runsphinx.py.in

@@ -40,7 +40,7 @@ def main(sysarg):
                            "Use -h for help" % ' '.join(args))
 
     # Update sys path if we need to
-    update_path(opts.mantidpath)
+    update_path()
 
     # Find test files
     testpaths = find_test_files(SRC_DIR, opts.testinclude)
@@ -102,9 +102,6 @@ def parseargs(arglist):
     """
     parser = OptionParser(usage="Usage: %prog [options]",
                           conflict_handler='error')
-    parser.add_option("-m", "--mantidpath", dest="mantidpath",
-                      help="Location of mantid package. Has no effect if run inside MantidPlot (default='%s')" % BUILD_DIR,
-                      default=BUILD_DIR)
     parser.add_option("-R", "--tests-regex", dest="testinclude",
                       help="Regex specifying which tests to run. It is matched against the "
                       "filename when considering whether to run a test.")
@@ -112,13 +109,10 @@ def parseargs(arglist):
 
 #-----------------------------------------------------------------------------------------------
 
-def update_path(mantidpath):
+def update_path():
     """
     If not inside MantidPlot (current check is whether we can import _qti)
     then insert given path as first directory in sys.path
-
-    Args:
-      mantidpath (str): A string giving the location of the mantid module
     """
     try:
         import _qti
@@ -126,13 +120,19 @@ def update_path(mantidpath):
     except ImportError:
         gui = False
 
+
     # If it's MantidPlot then we already know what our paths should be so ignore it
     if gui:
         return
 
-    # add 'bin' if the subdirectory exists and isn't named
-    if os.path.split(mantidpath)[-1] != 'bin':
-        if os.path.isdir(os.path.join(mantidpath, 'bin')):
+    # the python wrapper sets this environment variable
+    mantidpath = os.environ.get('MANTIDPATH', None)
+
+    # otherwise try to expand based off of information in cmake
+    if mantidpath is None or len(mantidpath) == 0:
+        mantidpath = BUILD_DIR
+        if os.path.split(mantidpath)[-1] != 'bin' and \
+           os.path.isdir(os.path.join(mantidpath, 'bin')):
             mantidpath = os.path.join(mantidpath, 'bin')
 
     # check for directory