fileserver: First attempt to fix failing test on Linux

[mholt]

I think I updated the wrong test case before. I don't have Linux handy so it's going to be trial-and-error until we can figure this out.

This is a new test case. If I recall correctly, we had problems with .PHP (non-lowercased path splits) that led to unfavorable handling of those requests in the past.

[mholt]

This test might only pass on case-insensitive file systems.

[Vigilans]

I debugged the matcher_test, the failure occured after the os.Stat call:

caddy/modules/caddyhttp/fileserver/matcher.go

Lines 255 to 267 in af5c148

	func strictFileExists(file string) bool {
	stat, err := os.Stat(file)
	if err != nil {
	// in reality, this can be any error
	// such as permission or even obscure
	// ones like "is not a directory" (when
	// trying to stat a file within a file);
	// in those cases we can't be sure if
	// the file exists, so we just treat any
	// error as if it does not exist; see
	// https://stackoverflow.com/a/12518877/1048862
	return false
	}

Here it tried to stat testdata/foo.php.PHP/index.php, but linux's file system is case sensitive:

caddy/modules/caddyhttp/fileserver/testdata$ ls
foo.php.php  index.php  notphp.php.txt  remote.php

So the flow fell into err != nil block and false was returned.

[mholt]

Thank you @Vigilans ! I bypassed that part of the code for the test in the end so it won't matter what FS it runs on.