Enforce literals in certain macros

[morrisonlevi]

The zend_string_equals_literal_ci and zend_string_equals_literal
macros are designed only for literals. This is a standards compliant
trick to ensure they are literals. It relies on the fact that two
adjacent string literals are concatenated. For example, these are the
same:

"Hello" " world"
"Hello world"

Since literals are ensured, use sizeof(...) - 1 instead of strlen.

I spot checked usages visually, but running the CI in case it finds any
non-literal uses.

[morrisonlevi]

The Travis CI job failure is concerning, though I don't think it's related to this PR. It's short, so I'll just copy its contents:

--TEST--
Test file_exists() function : usage variations
--CREDITS--
Dave Kelsey <[email protected]>
--FILE--
<?php
echo "*** Testing file_exists() : usage variations ***\n";

var_dump(file_exists(false));
var_dump(file_exists(''));
var_dump(file_exists(' '));
var_dump(file_exists('|'));
echo "Done";
?>
--EXPECT--
*** Testing file_exists() : usage variations ***
bool(false)
bool(false)
bool(false)
bool(false)
Done

Here's the diff:

========DIFF========
     *** Testing file_exists() : usage variations ***
     bool(false)
004+ bool(true)
     bool(false)
005- bool(false)
     Done
========DONE========
FAIL Test file_exists() function : usage variations [ext/standard/tests/file/file_exists_variation1.phpt] 
=====================================================================