GUACAMOLE-1181: Warn users if the internal behavior of their version of FreeRDP cannot be tested and may be unreliable.

configure.ac

@@ -623,6 +623,34 @@ then
 
 fi
 
+# It is difficult or impossible to test for variations in FreeRDP behavior in
+# between releases, as the change in behavior may not (yet) be associated with
+# a corresponding change in version number and may not have any detectable
+# effect on the FreeRDP API
+if test "x${have_freerdp2}" = "xyes"
+then
+
+    AC_MSG_CHECKING([whether FreeRDP appears to be a development version])
+    AC_EGREP_CPP([\"[0-9]+\\.[0-9]+\\.[0-9]+(-rc[0-9]+)?\"], [
+
+        #include <freerdp/version.h>
+        FREERDP_VERSION_FULL
+
+    ],
+    [AC_MSG_RESULT([no])],
+    [AC_MSG_RESULT([yes])]
+    [AC_MSG_WARN([
+  --------------------------------------------
+   You are building against a development version of FreeRDP. Non-release
+   versions of FreeRDP may have differences in behavior that are impossible to
+   check for at build time. This may result in memory leaks or other strange
+   behavior.
+
+   *** PLEASE USE A RELEASED VERSION OF FREERDP IF POSSIBLE ***
+  --------------------------------------------])])
+
+fi
+
 # Variation in memory internal allocation/free behavior for bitmaps
 if test "x${have_freerdp2}" = "xyes"
 then