fix wrongly used shell syntax on tests in configure.ac

configure.ac

@@ -285,7 +285,7 @@ AM_CONDITIONAL([WITH_FREQUENT_TAGS], [test x$enable_frequent_tag_generation != x
 
 dnl Check if doxygen is available
 AC_CHECK_PROGS([DOXYGEN], [doxygen], [no])
-AS_IF([ test "x$DOXYGEN" == x ],
+AS_IF([ test "x$DOXYGEN" = x ],
     [AC_MSG_WARN([Doxygen not found - continue without Doxygen support])],
     [AM_CONDITIONAL([HAVE_DOXYGEN], [ test "x$DOXYGEN" != xno ])
     dnl If you like to see verbose doxygen traces use this
@@ -296,15 +296,15 @@ AS_IF([ test "x$DOXYGEN" == x ],
     	[enable_verbose_doxygen=no])
     AM_CONDITIONAL([WITH_VERBOSE_DOXYGEN], [ test x$enable_verbose_doxygen != xno ])
     dnl propagate the doxygen verbose level to distribution
-    AS_IF([ test x$enable_verbose_doxygen == xyes ],
+    AS_IF([ test x$enable_verbose_doxygen = xyes ],
           [AC_SUBST([MSTRO_CONF_DOXY_VERBOSE], [--enable-verbose-doxygen])])
     AC_CHECK_PROGS([DOT], [dot], [no])
-    AS_IF([ test "x$DOT" == xno ],
+    AS_IF([ test "x$DOT" = xno ],
           [AC_MSG_WARN([Doxygen needs dot to generate graphs. Your documentation may be incomplete.])
           AC_SUBST([HAVE_DOT], [NO])],
           [AC_SUBST([HAVE_DOT], [YES])])
     AC_CHECK_PROGS([PDFLATEX], [pdflatex], [no])
-    AS_IF([ test "x$PDFLATEX" == xno ],
+    AS_IF([ test "x$PDFLATEX" = xno ],
           [AC_MSG_WARN([Doxygen needs pdflatex program for a better build, it is part of TeX http://www.tug.org/texlive/acquire-netinstall.html])
           AC_SUBST([HAVE_PDFLATEX], [NO])],
           [AC_SUBST([HAVE_PDFLATEX], [YES])])