Include Posix-compliant header for strcasecmp().

gcc has apparently merged this function in string.h but Posix specifies that it should be in strings.h.  FreeBSD at at least is sticking to the standard.

In the long run it might be better to implement our own strcasecmp() function but for now just add the header.

Suggested by ucando.

doc/xml/release.xml

@@ -38,6 +38,14 @@
 
                         <p>Update address lookup in C TLS client to use modern methods.</p>
                     </release-item>
+
+                    <release-item>
+                        <release-item-contributor-list>
+                            <release-item-ideator id="ucando"/>
+                        </release-item-contributor-list>
+
+                        <p>Include Posix-compliant header for <code>strcasecmp()</code>.</p>
+                    </release-item>
                 </release-improvement-list>
 
                 <release-development-list>
@@ -6394,6 +6402,11 @@
             <contributor-id type="github">seadba</contributor-id>
         </contributor>
 
+        <contributor id="ucando">
+            <contributor-name-display>ucando</contributor-name-display>
+            <contributor-id type="github">ucando</contributor-id>
+        </contributor>
+
         <contributor id="uspen">
             <contributor-name-display>uspen</contributor-name-display>
             <contributor-id type="github">uspen</contributor-id>

src/common/io/tls/client.c

@@ -5,6 +5,7 @@ TLS Client
 #include <netdb.h>
 #include <stdio.h>
 #include <string.h>
+#include <strings.h>
 #include <sys/socket.h>
 #include <unistd.h>