Fix detection of libedit on BSD

Since libedit originates from NetBSD, this and other BSDs use the
official version while Linux distributions tend to use the
autotoolized fork. The official version does not install a .pc file so
we cannot rely exclusively on pkg-config for detection.

FS-6408
Signed-off-by: Travis Cross <tc@traviscross.com>

configure.ac

@@ -1131,13 +1131,14 @@ PKG_CHECK_MODULES([YAML], [yaml-0.1 >= 0.1.4],[
 AC_ARG_ENABLE(core-libedit-support,     
   [AS_HELP_STRING([--disable-core-libedit-support], [Compile without libedit Support])])
 
-case x$enable_core_libedit_support in
-  xno) ;;
-  xyes|*)
-    PKG_CHECK_MODULES([LIBEDIT], [libedit >= 2.11],,
-      [AC_MSG_ERROR([You need to either install libedit-dev (>= 2.11) or configure with --disable-core-libedit-support])])
-    ;;
-esac
+AS_IF([test "x$enable_core_libedit_support" != "xno"],[
+  PKG_CHECK_MODULES([LIBEDIT], [libedit >= 2.11],,[
+    AC_MSG_RESULT([no])
+    AC_CHECK_LIB([edit], [el_line], [LIBEDIT_LIBS=-ledit])
+    AC_CHECK_HEADER([histedit.h], [], [unset LIBEDIT_LIBS])
+    AS_IF([test "x$LIBEDIT_LIBS" = "x"], [
+      AC_MSG_ERROR([You need to either install libedit-dev (>= 2.11) or configure with --disable-core-libedit-support])
+      ])])])
 
 AS_IF([test "x$enable_core_libedit_support" != "xno"], [
   # If making changes here, don't forget to run autoheader and