Fix running executables without extension on Win

Thanks to filterfalse.
State that exe completion doesn't give full paths

On Windows.
Merge branch 'fix-ext-commands-running-on-win'
Separate file and stream read lines functions

Automatic choosing of stream type (seekable/non-seekable) doesn't work
on Windows.
Fix viewing of files with custom viewers on Win

Thanks to filterfalse.
Merge branch 'fix-view-viewing-on-win'