global 6.6.7 and earlier versions hardcode the use of a 7-year-old version
of SQLite. This patch adds an optional argument to `--with-sqlite3` to
allow linking against an external SQLite library, which should generally
Just Work, thanks to Dr. Richard Hipp's relentless commitment to backward
compatibility. (Plain `--with-sqlite3` still links against vendored SQLite.)

diff --git a/configure.ac b/configure.ac
index bc31bcc..eebbc46 100644
--- a/configure.ac
+++ b/configure.ac
@@ -217,14 +217,35 @@ dnl Use sqlite3 API.
 dnl
 AC_MSG_CHECKING(for sqlite3 support)
 AC_ARG_WITH(sqlite3,
-[  --with-sqlite3          use sqlite3 API ],
+[  --with-sqlite3[[=DIR]]    use sqlite3 API ],
 [
-	#LDFLAGS="$LDFLAGS -lsqlite3"
+	AM_CONDITIONAL(USE_SQLITE3_VENDORED, true)
+	if test "$withval" != no; then
+		case "$withval" in
+		''|yes)
+			;;
+		*)
+			if ! test -d "$withval"; then
+				AC_MSG_ERROR([directory $withval not found.])
+			fi
+			if ! test -r "$withval/include/sqlite3.h"; then
+				AC_MSG_ERROR([header $withval/include/sqlite3.h not found.])
+			fi
+			if ! test -r "$withval/lib/libsqlite3.so" && ! test -r "$withval/lib/libsqlite3.dylib"; then
+				AC_MSG_ERROR([library $withval/lib/libsqlite3.* not found.])
+			fi
+			AM_CONDITIONAL(USE_SQLITE3_VENDORED, false)
+			AM_CPPFLAGS="$AM_CPPFLAGS -I$withval/include"
+			LIBS="$LIBS -L$withval/lib -lsqlite3"
+			;;
+		esac
+	fi
 	AC_DEFINE(USE_SQLITE3,1,[Define if you use sqlite3 API.])
 	AM_CONDITIONAL(USE_SQLITE3, true)
 	AC_MSG_RESULT(yes)
 ],[
 	AM_CONDITIONAL(USE_SQLITE3, false)
+	AM_CONDITIONAL(USE_SQLITE3_VENDORED, false)
 	AC_MSG_RESULT(no)
 ])
 
@@ -379,6 +400,7 @@ AC_SUBST(POSIX_SORT)
 AC_SUBST(AM_CPPFLAGS)
 AC_SUBST(LDADD)
 AC_SUBST(LDFLAGS)
+AC_SUBST(LIBS)
 
 dnl
 dnl The definition of config variable skip and suffixes.
diff --git a/libdb/Makefile.am b/libdb/Makefile.am
index dcccb1d..c51a5ca 100644
--- a/libdb/Makefile.am
+++ b/libdb/Makefile.am
@@ -16,7 +16,7 @@ INCS = btree.h db.h extern.h mpool.h queue.h compat.h
 SRCS = bt_close.c bt_conv.c bt_debug.c bt_delete.c bt_get.c bt_open.c bt_overflow.c \
         bt_page.c bt_put.c bt_search.c bt_seq.c bt_split.c bt_utils.c db.c mpool.c
 
-if USE_SQLITE3
+if USE_SQLITE3_VENDORED
 INCS += sqlite3.h
 SRCS += sqlite3.c
 AM_CPPFLAGS += -DSQLITE_THREADSAFE=0 -DSQLITE_OMIT_LOAD_EXTENSION