Remove some duplicate includes

[mknos]

I started with the command...

for f in `find . -name '*.c'`; do echo "FILE=$f"; fgrep '#include' $f | sort | uniq -d; done

Some results appear to be false positives because the .h files are written as templates; these are intended for inclusion multiple times:
ntlibfuncs.h
fsort_template.h
combine_path.h
program_areas.h
errors.h
lexer.h
compilation.h

Some other results were guarded by ifdef conditions. In cpp.cmod, pike_compiler.h appears in include list twice. In fdlib.c, sys/uio.h is included (if available) at the top of the file.