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

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

	$ cat ~/tmp/spatch/streq.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/streq.sp;

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

lib/valid.c

@@ -42,8 +42,8 @@ bool valid (const char *password, const struct passwd *ent)
 	 * routine is meant to waste CPU time.
 	 */
 
-	if ((NULL != ent->pw_name) && ('\0' == ent->pw_passwd[0])) {
-		if ('\0' == password[0]) {
+	if ((NULL != ent->pw_name) && streq(ent->pw_passwd, "")) {
+		if (streq(password, "")) {
 			return true;	/* user entered nothing */
 		} else {
 			return false;	/* user entered something! */
@@ -54,7 +54,7 @@ bool valid (const char *password, const struct passwd *ent)
 	 * If there is no entry then we need a salt to use.
 	 */
 
-	if ((NULL == ent->pw_name) || ('\0' == ent->pw_passwd[0])) {
+	if ((NULL == ent->pw_name) || streq(ent->pw_passwd, "")) {
 		salt = "xx";
 	} else {
 		salt = ent->pw_passwd;