Don't hardcode "plugins" as the subdirectory for plugins in many
places.

	modified:   config-win32.h
	modified:   configure.ac
	modified:   plugins/checksum/Makefile.am
	modified:   plugins/doat/Makefile.am
	modified:   plugins/fishlim/Makefile.am
	modified:   plugins/perl/Makefile.am
	modified:   plugins/python/Makefile.am
	modified:   plugins/sysinfo/Makefile.am
	modified:   plugins/xdcc/Makefile.am
	modified:   src/common/plugin.c
	modified:   src/fe-text/fe-text.c