pbx_lua: Add LUA_VERSIONS environment variable to ./configure.

On Gentoo it's possible to have multiple lua versions installed, all
with a path of /usr, so it's not possible to use the current --with-lua
option to determisticly pin to a specific version as is required by the
Gentoo PMS standards.

This environment variable allows to lock to specific versions,
unversioned check will be skipped if this variable is supplied.

Change-Id: I8c403eda05df25ee0193960262ce849c7d2fd088
Signed-off-by: Jaco Kroon <jaco@uls.co.za>

configure

@@ -1051,6 +1051,7 @@ PBX_MISDN
 MISDN_DIR
 MISDN_INCLUDE
 MISDN_LIB
+LUA_VERSIONS
 PBX_LUA
 LUA_DIR
 LUA_INCLUDE
@@ -1477,6 +1478,7 @@ CCC
 CXXCPP
 JANSSON_CONFIGURE_OPTS
 PJPROJECT_CONFIGURE_OPTS
+LUA_VERSIONS
 PKG_CONFIG
 PKG_CONFIG_PATH
 PKG_CONFIG_LIBDIR
@@ -2235,6 +2237,8 @@ Some influential environment variables:
               Additional configure options to pass to bundled jansson
   PJPROJECT_CONFIGURE_OPTS
               Additional configure options to pass to bundled pjproject
+  LUA_VERSIONS
+              A space separated list of target lua versions to test.
   PKG_CONFIG  path to pkg-config utility
   PKG_CONFIG_PATH
               directories to add to pkg-config's search path
@@ -29633,7 +29637,7 @@ fi
 
 
 
-for ver in 5.4 5.3 5.2 5.1; do
+for ver in ${LUA_VERSIONS:-5.4 5.3 5.2 5.1}; do
 
 if test "x${PBX_LUA}" != "x1" -a "${USE_LUA}" != "no"; then
    pbxlibdir=""
@@ -29744,6 +29748,7 @@ fi
 done
 
 # Some distributions (like openSUSE and NetBSD) remove the 5.x suffix.
+if test "x${LUA_VERSIONS}" = "x"; then
 
 if test "x${PBX_LUA}" != "x1" -a "${USE_LUA}" != "no"; then
    pbxlibdir=""
@@ -29840,6 +29845,7 @@ _ACEOF
 fi
 
 
+fi
 
 # Accept either RADIUS client library, their APIs are fully compatible,
 # just different header filenames and different SONAMEs