[configure] require gnutls>=2.1.7
[configure] require gnutls>=2.1.7

noted by Nguyen Thai Ngoc Duy in bug 581342

fanc999/libsoup,fanc999/libsoup,ahmedammar/platform_external_gst_libsoup,fanc999/libsoup,jwendell/libsoup,ahmedammar/platform_external_gst_libsoup,ahmedammar/platform_external_gst_libsoup,Distrotech/libsoup,Distrotech/libsoup,jwendell/libsoup,jwendell/libsoup,jwendell/libsoup,Distrotech/libsoup,jwendell/libsoup,fanc999/libsoup,Distrotech/libsoup,Distrotech/libsoup,fanc999/libsoup