* config.make.in: Add have-libcap.
* configure.in: Check for libcap.
* nscd/Makefile (selinux-LIBS): Add -lcap if possible.
* nscd/connections.c (finish_drop_privileges): When libcap is available
call preserve_capabilities and install_real_capabilities.
* nscd/selinux.c: Define preserve_capabilities and
install_real_capabilities.
* nscd/selinux.h: Declare preserve_capabilities and
install_real_capabilities.