Merge of r4870, r4871, r4890, r4895: minor fixes.

Merge of r4870, r4871, r4890, r4895: minor fixes.

*) Made sure to initialize the entire ngx_file_t structure.
   Found by Coverity.

*) Correct plural form for "path" in the whole source base.

*) Removed conditional compilation from waitpid() error test.

   There are reports that call to a signal handler for an exited process
   despite waitpid() already called for the process may happen on Linux
   as well.

*) Style, parentheses instead of braces in misc/GNUMakefile.