Add auto mode to lmdb that will fallback to embedded version if shared lmdb is...

Add auto mode to lmdb that will fallback to embedded version if shared lmdb is too old or non-existent

configure.ac

@@ -337,7 +337,7 @@ AC_ARG_WITH([lmdb],
     AC_HELP_STRING([--with-lmdb=[DIR]], [Link with external LMDB (>= $lmdb_MIN_VERSION_STRING)]),[
     with_lmdb=$withval
     ],[
-    with_lmdb=yes
+    with_lmdb=auto
     ])
 
 have_lmdb=no
@@ -365,10 +365,11 @@ AS_IF([test "$with_lmdb" != "no"],[
               AC_MSG_ERROR([lmdb headers not found in `$try_lmdb', is your installation complete?])])
           AC_COMPUTE_INT(lmdb_VERSION_FULL, MDB_VERSION_FULL, [#include <lmdb.h>],
 	      AC_MSG_ERROR([Unable to determine lmdb version from MDB_VERSION_FULL]))
-	  AS_IF([test "$lmdb_VERSION_FULL" -lt "$lmdb_MIN_VERSION_FULL"],[
-	      AC_MSG_ERROR([lmdb version $lmdb_MIN_VERSION_STRING or higher required or compile with embedded lmdb (--with-lmdb=no)])])
-          lmdb_LIBS="$lmdb_LIBS -llmdb"
-          have_lmdb=yes
+	  AS_IF([test "$lmdb_VERSION_FULL" -ge "$lmdb_MIN_VERSION_FULL"],[
+              lmdb_LIBS="$lmdb_LIBS -llmdb"
+              have_lmdb=yes],[
+	      AC_MSG_WARN([lmdb version 0.9.15 and higher not found, using embedded version])
+	      ])
           break 
           ])
 
@@ -382,7 +383,7 @@ AS_IF([test "$with_lmdb" != "no"],[
     LIBS="$save_LIBS"
 
     # fail the configure if we haven't found lmdb library in the system
-    AS_IF([test "$have_lmdb" = "no"],[
+    AS_IF([test "$with_lmdb" != "auto" -a "$have_lmdb" = "no"],[
         AC_MSG_ERROR([shared lmdb library not found])
 	])
     ])