--disable-doc is not parsed correctly by configure

[saraedum]

Currently, configure --disable-doc makes fflas-ffpack try to build the documentation. The reason is that AC_ARG_ENABLE is not used correctly; that's because it's AC_ARG_ENABLE(name, help, help, present, missing) and not AC_ARG_ENABLE(name, help, help, enable, disable). Something like this should fix it:

diff --git a/macros/fflas-ffpack-doc.m4 b/macros/fflas-ffpack-doc.m4
index c225398..6adb7fe 100644
--- a/macros/fflas-ffpack-doc.m4
+++ b/macros/fflas-ffpack-doc.m4
@@ -47,25 +47,26 @@ AC_ARG_WITH(doxygen,
                DOXYGEN_PATH="$PATH"
            ])

-AC_ARG_ENABLE(doc,[AC_HELP_STRING([--enable-doc], [Enable building documentation])],
-[
-AC_MSG_RESULT(yes)
-AC_MSG_CHECKING(whether doxygen works)
-export PATH=$DOXYGEN_PATH
-(doxygen --version) < /dev/null > /dev/null 2>&1 || {
-       AC_MSG_RESULT(no)
-       echo
-       echo "You must have doxygen installed to create documentation for"
-       echo "FFLAS-FFPACK. This error only happens if you use --enable-doc."
-       echo "Download the appropriate package for your distribution, or get"
-       echo "the source tarball from http://www.stack.nl/~dimitri/doxygen/"
-       exit -1
-}
-AC_MSG_RESULT(yes)
-AM_CONDITIONAL(FFLASFFPACK_BUILD_DOC, true)
-],
-[
-AC_MSG_RESULT(no)
-AM_CONDITIONAL(FFLASFFPACK_BUILD_DOC, false)
-])
+AC_ARG_ENABLE(doc,[AC_HELP_STRING([--enable-doc], [Enable building documentation])])
+
+AS_IF([test x"$enable_doc" != "xno"],[
+  enable_doc=yes
+  AC_MSG_RESULT(yes)
+  AC_MSG_CHECKING(whether doxygen works)
+  export PATH=$DOXYGEN_PATH
+  (doxygen --version) < /dev/null > /dev/null 2>&1 || {
+    AC_MSG_RESULT(no)
+    echo
+    echo "You must have doxygen installed to create documentation for"
+    echo "FFLAS-FFPACK. This error only happens if you use --enable-doc."
+    echo "Download the appropriate package for your distribution, or get"
+    echo "the source tarball from http://www.stack.nl/~dimitri/doxygen/"
+    exit -1
+  }
+  AC_MSG_RESULT(yes)
+  AM_CONDITIONAL(FFLASFFPACK_BUILD_DOC, true)
+], [
+  AC_MSG_RESULT(no)
 ])
+
+AM_CONDITIONAL(FFLASFFPACK_BUILD_DOC, [test "x$enable_doc" = "xyes"])