configure.in: AC_PREREQ autoconf 2.60 or above
configure.in: AC_PREREQ autoconf 2.60 or above

This is to preclude regeneration of ./configure using a too-old
autoconf that mistreats e.g. the AC_COMPILE_IFELSE construct.

I'd like to exclude rhel4's 2.59, but it's not clear at what point the
combination of AC_ARG_ENABLE / AC_COMPILE_IFELSE as used here has
started working properly, so the actually required version number
may be closer to the current 2.69.

edwardt/pcp,wuliming/pcp,aeg-aeg/pcpfans,adfernandes/pcp,tjanez/pcp,tjanez/pcp,adfernandes/pcp,prasincs/pcp,prasincs/pcp,aeg-aeg/pcpfans,prasincs/pcp,wuliming/pcp,aeg-aeg/pcpfans,ryandoyle/pcp_original,wuliming/pcp,tjanez/pcp,aeg-aeg/pcpfans,edwardt/pcp,mbaldessari/pcp,tjanez/pcp,wuliming/pcp,aeg-aeg/pcpfans,tjanez/pcp,edwardt/pcp,prasincs/pcp,prasincs/pcp,andyvand/cygpcpfans,tjanez/pcp,adfernandes/pcp,aeg-aeg/pcpfans,prasincs/pcp,tjanez/pcp,andyvand/cygpcpfans,mbaldessari/pcp,edwardt/pcp,adfernandes/pcp,mbaldessari/pcp,ryandoyle/pcp_original,prasincs/pcp,adfernandes/pcp,andyvand/cygpcpfans,aeg-aeg/pcpfans,ryandoyle/pcp_original,adfernandes/pcp,mbaldessari/pcp,andyvand/cygpcpfans,edwardt/pcp,edwardt/pcp,ryandoyle/pcp_original,wuliming/pcp,mbaldessari/pcp,wuliming/pcp,mbaldessari/pcp,andyvand/cygpcpfans,ryandoyle/pcp_original,prasincs/pcp,wuliming/pcp,ryandoyle/pcp_original,andyvand/cygpcpfans,tjanez/pcp,edwardt/pcp,andyvand/cygpcpfans,adfernandes/pcp,edwardt/pcp,wuliming/pcp,andyvand/cygpcpfans,ryandoyle/pcp_original,adfernandes/pcp,aeg-aeg/pcpfans,ryandoyle/pcp_original