Fixed some typos and improved wording

doc/optimizations.txt

@@ -20,8 +20,8 @@ If you would like to add an additional optimization, refer to
 
     This list is partial.
 
-    The print_summary method allow several OpDBs and optimizers to list the optimization executed.
-    This allow to have an up-to-date list.
+    The print_summary method allows several OpDBs and optimizers to list the executed optimizations.
+    This makes it possible to have an up-to-date list.
 
     python -c 'import theano; theano.compile.FAST_RUN.optimizer.print_summary()'
 
@@ -255,6 +255,6 @@ Optimization                                              FAST_RUN  FAST_COMPILE
 
     local_log_softmax
         This is a stabilization optimization.
-        It can happen due to rounding problem that the softmax probability of one value get to 0.
-        Taking the log of 0, would generate -inf that will probably generate NaN later.
+        It can happen due to rounding errors that the softmax probability of one value gets to 0.
+        Taking the log of 0 would generate -inf that will probably generate NaN later.
         We return a closer answer.

theano/sandbox/cuda/__init__.py

@@ -393,11 +393,12 @@ def use(device,
             if device_properties(use.device_number)['regsPerBlock'] < 16384:
                 # We will try to use too much register per bloc at many places
                 # when there is only 8k register per multi-processor.
-                _logger.warning("You are probably using an old GPU."
-                                " We didn't optimize nor we support those GPU."
-                                " This mean GPU code will be slow AND will"
-                                " crash when we try to use feature/properties"
-                                " that your GPU don't support.")
+                _logger.warning(
+                        "You are probably using an old GPU, that Theano"
+                        " does not support."
+                        " This means GPU code will most likely be slow AND may"
+                        " crash when we try to use features"
+                        " that your GPU does not support.")
 
         except (EnvironmentError, ValueError, RuntimeError), e:
             _logger.error(("ERROR: Not using GPU."