Add curses header folder to include path
Use putenv for os_setenv

- In systems where setenv is not available, os_setenv() can use
  putenv
Rename variable eof to input_eof
Remove includes for os_unix.h
Dont report unsused variables with Mingw
Fix config.h.in for Mingw
FIXME: Remove cscope support
FIXME: did we want errno or not?