The file extension to mime type mapping *must* not depend on the file
extension's case for case-insensitive file systems, and *should* not
for case-sensitive file systems.

Don't unnecessarily truncate to milliseconds.

Closes GH-5760.

As of PHP 7.3.0, `sapi_cli_single_write()` is supposed to return `< 0`
on failure, but `fwrite()` returns a `size_t`, and signals error by
setting the stream's error indicator.  We have to cater to that.

Since the member is not used in `OnUpdateEol()` that's not really an
issue, but still it's confusing to apparently have two INI settings
targeting the same member.

On Windows, PATH_TRANSLATED may contain backslashes as well as slashes,
so we must not only check for `DEFAULT_SLASH`.

The `start` parameter of `php_cgi_ini_activate_user_config` is supposed
to hold the byte offset of the doc root in the given `path`.  However,
the current expression which fixes a potential type incompatibility
will ever only evaluate to zero or one, because it uses the *logical*
and operator (`&&`).  Furthermore we notice that subtracting one from
`doc_root_len` is not necessary, so there is even no need for the
`start` parameter at all.

This is the change from GH-5417 but for FPM. This was stripping the
last character from the doc_root. Given how it is used, this should
be harmless, but let's make it less confusing...