Gracefully disable docs if Sphinx is not found.

- Also fixes a typo in the search paths in FindSphinx.cmake.

Change-Id: I8da50ffd85358f7e67445b02eabfc9cf57c97935

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index e33a43e..e40dd17 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -188,7 +188,7 @@
   # Apple claims that the BLAS call dsyrk_ is a private API, and will not allow you
   # to submit to the Apple Store if the symbol is present.
   UPDATE_CACHE_VARIABLE(LAPACK OFF)
-  
+
   MESSAGE(STATUS "Building for iOS: SuiteSparse, CXSparse, LAPACK, gflags, and OpenMP are not available.")
 
   UPDATE_CACHE_VARIABLE(BUILD_EXAMPLES OFF)
@@ -786,11 +786,16 @@
 ADD_SUBDIRECTORY(internal/ceres)
 
 IF (BUILD_DOCUMENTATION)
-  MESSAGE("-- Documentation building is enabled")
-
-  # Generate the User's Guide (html).
-  # The corresponding target is UserGuide, but is included in ALL.
-  ADD_SUBDIRECTORY(docs)
+  FIND_PACKAGE(Sphinx QUIET)
+  IF (NOT SPHINX_FOUND)
+    MESSAGE("-- Failed to find Sphinx, disabling build of documentation.")
+    UPDATE_CACHE_VARIABLE(BUILD_DOCUMENTATION OFF)
+  ELSE()
+    # Generate the User's Guide (html).
+    # The corresponding target is ceres_docs, but is included in ALL.
+    MESSAGE("-- Build the HTML documentation.")
+    ADD_SUBDIRECTORY(docs)
+  ENDIF()
 ENDIF (BUILD_DOCUMENTATION)
 
 IF (BUILD_EXAMPLES)

cmake/FindSphinx.cmake

diff --git a/cmake/FindSphinx.cmake b/cmake/FindSphinx.cmake
index 86c172e..aebf615 100644
--- a/cmake/FindSphinx.cmake
+++ b/cmake/FindSphinx.cmake
@@ -54,7 +54,7 @@
                  PATHS
                    /usr/bin
                    /usr/local/bin
-                   /opt/loca/bin
+                   /opt/local/bin
                  DOC "Sphinx documentation generator")
   ENDFOREACH ()
 ENDIF ()