Allow people without MOPAC to run RMG.

The 'check that you can find Mopac' test was being run on importing rmgpy.qm.mopac
which apparently is done whether or not QM is being used.

Now it is postponed until you are about to run a job.
I did the same for Gaussian while I was at it.

Author: rwest

rmgpy/qm/gaussian.py

@@ -33,8 +33,14 @@ class Gaussian:
     successKeys = [
                    'Normal termination of Gaussian'
                   ]
-    
+ 
+    def testReady(self):
+        if not os.path.exists(self.executablePath):
+            raise Exception("Couldn't find Gaussian executable at {0}. Try setting your GAUSS_EXEDIR environment variable.".format(self.executablePath))
+
+   
     def run(self):
+        self.testReady()
         # submits the input file to Gaussian
         process = Popen([self.executablePath, self.inputFilePath, self.outputFilePath])
         process.communicate()# necessary to wait for executable termination!

rmgpy/qm/mopac.py

@@ -18,7 +18,6 @@ class Mopac:
     inputFileExtension = '.mop'
     outputFileExtension = '.out'
     executablePath = os.path.join(os.getenv('MOPAC_DIR', default="/opt/mopac") , 'MOPAC2012.exe')
-    assert os.path.exists(executablePath), "Couldn't find MOPAC 2009 executable at {0}. Try setting your MOPAC_DIR environment variable.".format(executablePath)
 
     usePolar = False #use polar keyword in MOPAC
 
@@ -48,8 +47,13 @@ class Mopac:
                    'DESCRIPTION OF VIBRATIONS',
                   ]
 
+    def testReady(self):
+        if not os.path.exists(self.executablePath):
+            raise Exception("Couldn't find MOPAC 2012 executable at {0}. Try setting your MOPAC_DIR environment variable.".format(self.executablePath))
+
 
     def run(self):
+        self.testReady()
         # submits the input file to mopac
         process = Popen([self.executablePath, self.inputFilePath])
         process.communicate()# necessary to wait for executable termination!