lib/, src/: Use !streq() instead of its pattern

Except for the added (and sorted) includes, the removal of redundant
parentheses, and a few non-string cases that I've left out of the
change, this patch can be approximated with the following semantic
patch:

	$ cat ~/tmp/spatch/strneq.sp
	@@
	expression s;
	@@

	- '\0' != *s
	+ !streq(s, "")

	@@
	expression s;
	@@

	- '\0' != s[0]
	+ !streq(s, "")

	@@
	expression s;
	@@

	- *s != '\0'
	+ !streq(s, "")

	@@
	expression s;
	@@

	- s[0] != '\0'
	+ !streq(s, "")

	$ find contrib/ lib* src/ -type f \
	| xargs spatch --in-place --sp-file ~/tmp/spatch/strneq.sp;

Signed-off-by: Alejandro Colomar <alx@kernel.org>

lib/fields.c

@@ -18,6 +18,7 @@
 #include "prototypes.h"
 #include "string/strchr/stpspn.h"
 #include "string/strchr/strrspn.h"
+#include "string/strcmp/streq.h"
 #include "string/strtok/stpsep.h"
 
 
@@ -47,7 +48,7 @@ int valid_field (const char *field, const char *illegal)
 	}
 
 	/* Search if there are non-printable or control characters */
-	for (cp = field; '\0' != *cp; cp++) {
+	for (cp = field; !streq(cp, ""); cp++) {
 		unsigned char c = *cp;
 		if (!isprint (c)) {
 			err = 1;
@@ -86,7 +87,7 @@ change_field(char *buf, size_t maxsize, const char *prompt)
 	if (stpsep(newf, "\n") == NULL)
 		return;
 
-	if ('\0' != newf[0]) {
+	if (!streq(newf, "")) {
 		/*
 		 * Remove leading and trailing whitespace.  This also
 		 * makes it possible to change the field to empty, by