maint: fix spelling error in hacking

* HACKING: STRCASEEQ is case insensitive.
* docs/hacking.html.in: Likewise.

HACKING

@@ -222,7 +222,7 @@ one of the following semantically named macros
      STREQ(a,b)
      STRNEQ(a,b)
 
-  - For case sensitive equality:
+  - For case insensitive equality:
      STRCASEEQ(a,b)
      STRCASENEQ(a,b)
 
@@ -231,7 +231,7 @@ one of the following semantically named macros
      STREQLEN(a,b,n)
      STRNEQLEN(a,b,n)
 
-  - For case sensitive equality of a substring:
+  - For case insensitive equality of a substring:
 
      STRCASEEQLEN(a,b,n)
      STRCASENEQLEN(a,b,n)

docs/hacking.html.in

@@ -256,7 +256,7 @@
 </pre>
       </li>
 
-      <li><p>For case sensitive equality:</p>
+      <li><p>For case insensitive equality:</p>
         <pre>
      STRCASEEQ(a,b)
      STRCASENEQ(a,b)
@@ -271,7 +271,7 @@
 </pre>
       </li>
 
-      <li><p>For case sensitive equality of a substring:</p>
+      <li><p>For case insensitive equality of a substring:</p>
 
         <pre>
      STRCASEEQLEN(a,b,n)