Description: use system-installed mathjx instead of downloading from the net
Forwarded: https://github.com/opencv/opencv/pull/9866

--- a/doc/Doxyfile.in
+++ b/doc/Doxyfile.in
@@ -174,7 +174,7 @@
 FORMULA_TRANSPARENT    = YES
 USE_MATHJAX            = YES
 MATHJAX_FORMAT         = HTML-CSS
-MATHJAX_RELPATH        = http://cdn.mathjax.org/mathjax/latest
+MATHJAX_RELPATH        = @OPENCV_MATHJAX_RELPATH@
 MATHJAX_EXTENSIONS     = TeX/AMSmath TeX/AMSsymbols
 MATHJAX_CODEFILE       = @CMAKE_CURRENT_SOURCE_DIR@/mymath.js
 SEARCHENGINE           = YES
--- a/doc/CMakeLists.txt
+++ b/doc/CMakeLists.txt
@@ -36,6 +36,8 @@
   list(APPEND blacklist "ts" "java" "python2" "python3" "world" "contrib_world")
   unset(CMAKE_DOXYGEN_TUTORIAL_CONTRIB_ROOT)
 
+  set(OPENCV_MATHJAX_RELPATH "http://cdn.mathjax.org/mathjax/latest" CACHE STRING "URI to a MathJax installation")
+
   # gathering headers
   set(paths_include)
   set(paths_doc)
