Initialize SAGE_ENABLE_... properly, add 'configure --disable-notebook'

Author: Matthias Koeppe

bootstrap

@@ -84,7 +84,7 @@ bootstrap () {
     # initialize SAGE_ENABLE... options for standard packages
     for pkgname in $(./sage --package list :standard: | sort); do
         spkg_configures="$spkg_configures
-AC_SUBST(SAGE_ENABLE_$pkgname, [yes])"
+AS_VAR_SET_IF([SAGE_ENABLE_$pkgname], [], [AS_VAR_SET([SAGE_ENABLE_$pkgname], [yes])])"
     done
     # --enable-SPKG options
     for pkgname in $(./sage --package list :optional: :experimental: | sort); do

configure.ac

@@ -416,6 +416,14 @@ AS_IF([test "x$enable_download_from_upstream_url" = "xyes"], [
 ])
 AC_SUBST([SAGE_SPKG_OPTIONS])
 
+AC_ARG_ENABLE([notebook],
+  AS_HELP_STRING([--disable-notebook],
+                 [disable build of the Jupyter notebook and related packages]), [
+    for pkg in notebook nbconvert nbformat tornado terminado send2trash prometheus_client mistune traitlets pandocfilters bleach defusedxml jsonschema widgetsnbextension jupyter_jsmol; do
+      AS_VAR_SET([SAGE_ENABLE_$pkg], [$enableval])
+    done
+  ])
+
 SAGE_SPKG_COLLECT()
 
 dnl AC_CONFIG_HEADERS([config.h])

m4/sage_spkg_collect.m4

@@ -164,7 +164,14 @@ for DIR in $SAGE_ROOT/build/pkgs/*; do
     base)
         message="came preinstalled with the SageMath tarball"
         ;;
-    standard|optional|experimental)
+    standard)
+        AS_VAR_IF([SAGE_ENABLE_]${SPKG_NAME}, [yes], [
+            message="$SPKG_TYPE, will be installed as an SPKG"
+        ], [
+            message="$SPKG_TYPE, but disabled using configure option"
+        ])
+        ;;
+    optional|experimental)
         AS_VAR_IF([SAGE_ENABLE_]${SPKG_NAME}, [yes], [
             message="$SPKG_TYPE, will be installed as an SPKG"
         ], [