Fix some doc generation warnings/errors

doc/developer/compat.txt

@@ -20,12 +20,14 @@ but here are some guidelines for the major things to be aware of.
   syntax:
 
     .. code-block:: python
+
         except Exception as e:
            ...
 
 * No tuple-unpacking in the argument list:
 
     .. code-block:: python
+
         def f(a, (b, c)):  # wrong
             ...
 
@@ -35,6 +37,7 @@ but here are some guidelines for the major things to be aware of.
 * Always use ``print(...)`` as a function, and add
 
     .. code-block:: python
+
         from __future__ import print_function
 
   At the top of files that use ``print``, above all other imports.

doc/library/compile/nanguardmode.txt

 
 .. _nanguardmode:
 
-=================
+===================
 :mod:`nanguardmode`
-=================
+===================
 
 .. module:: nanguardmode
    :platform: Unix, Windows

doc/tutorial/debug_faq.txt

@@ -296,7 +296,7 @@ Tips:
 
 
 "Why does my GPU function seem to be slow?"
-------------------------------------------
+-------------------------------------------
 
 When you compile a theano function, if you do not get the speedup that you expect over the 
 CPU performance of the same code. It is oftentimes due to the fact that some Ops might be running
@@ -307,7 +307,7 @@ options:
 * ``warn``: Raise a warning
 * ``pdb``: Stop with a pdb in the computational graph during the compilation
 * ``raise``: Raise an error,
-if there is a CPU Op in the computational graph.
+  if there is a CPU Op in the computational graph.
 
 It is possible to use this mode by providing the flag in THEANO_FLAGS, such as:
 ``THEANO_FLAGS="float32,device=gpu,assert_no_cpu_op='raise'" python test.py``