Tighten some library checks (check for header files as well as libraries)
Tighten some library checks (check for header files as well as libraries)

Original commit message from CVS:
Tighten some library checks (check for header files as well as libraries)
Also, clean up structure slightly: put all AC_DEFINEs for feature checks
into the appropriate section at end.  This structure allows user parameter
code which overrides the feature selection to be kept together in a section
after the feature checks but before the AC_DEFINES and AM_CONDITIONALs.

ahmedammar/platform_external_gst_gstreamer,drothlis/gstreamer,justinjoy/gstreamer,collects/gstreamer,lubosz/gstreamer,ensonic/gstreamer,justinjoy/gstreamer,justinjoy/gstreamer,Lachann/gstreamer,lubosz/gstreamer,krieger-od/gstreamer,jpxiong/gstreamer,cablelabs/gstreamer,surround-io/gstreamer,drothlis/gstreamer,mrchapp/gstreamer,StreamUtils/gstreamer,Lachann/gstreamer,mparis/gstreamer,lubosz/gstreamer,jpxiong/gstreamer,drothlis/gstreamer,jpxiong/gstreamer,cfoch/gstreamer,jpxiong/gstreamer,jpxiong/gstreamer,krieger-od/gstreamer,mrchapp/gstreamer,jpakkane/gstreamer,mrchapp/gstreamer,drothlis/gstreamer,collects/gstreamer,ylatuya/gstreamer,jpakkane/gstreamer,magcius/gstreamer,cablelabs/gstreamer,surround-io/gstreamer,StreamUtils/gstreamer,ylatuya/gstreamer,lovebug356/gstreamer,jpakkane/gstreamer,justinjoy/gstreamer,ensonic/gstreamer,magcius/gstreamer,shelsonjava/gstreamer,ensonic/gstreamer,krichter722/gstreamer,magcius/gstreamer,Lachann/gstreamer,mparis/gstreamer,centricular/gstreamer,ahmedammar/platform_external_gst_gstreamer,collects/gstreamer,lovebug356/gstreamer,cablelabs/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,centricular/gstreamer,collects/gstreamer,krieger-od/gstreamer,ylatuya/gstreamer,krichter722/gstreamer,ahmedammar/platform_external_gst_gstreamer,Distrotech/gstreamer,Lachann/gstreamer,cfoch/gstreamer,Distrotech/gstreamer,mparis/gstreamer,cfoch/gstreamer,krieger-od/gstreamer,cfoch/gstreamer,mrchapp/gstreamer,magcius/gstreamer,ensonic/gstreamer,jpakkane/gstreamer,lovebug356/gstreamer,Distrotech/gstreamer,shelsonjava/gstreamer,centricular/gstreamer,krichter722/gstreamer,Distrotech/gstreamer,surround-io/gstreamer,StreamUtils/gstreamer,shelsonjava/gstreamer,shelsonjava/gstreamer,centricular/gstreamer,cablelabs/gstreamer,krieger-od/gstreamer,shelsonjava/gstreamer,surround-io/gstreamer,cfoch/gstreamer,ensonic/gstreamer,ylatuya/gstreamer,cablelabs/gstreamer,lovebug356/gstreamer,StreamUtils/gstreamer,mrchapp/gstreamer,ahmedammar/platform_external_gst_gstreamer,mparis/gstreamer,drothlis/gstreamer,lovebug356/gstreamer,Lachann/gstreamer,ylatuya/gstreamer,centricular/gstreamer,Distrotech/gstreamer,justinjoy/gstreamer,krichter722/gstreamer,collects/gstreamer,lubosz/gstreamer,mparis/gstreamer,magcius/gstreamer,ahmedammar/platform_external_gst_gstreamer,lubosz/gstreamer,surround-io/gstreamer,jpakkane/gstreamer