strcasecompare: is the new name for strequal()

... to make it less likely that we forget that the function actually
does case insentive compares. Also replaced several invokes of the
function with a plain strcmp when case sensitivity is not an issue (like
comparing with "-").

lib/strcase.c

@@ -0,0 +1,79 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 1998 - 2016, Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.haxx.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ***************************************************************************/
+
+#include "curl_setup.h"
+
+#ifdef HAVE_STRINGS_H
+#include <strings.h>
+#endif
+
+#include "strcase.h"
+
+/*
+ * @unittest: 1301
+ */
+int curl_strcasecompare(const char *first, const char *second)
+{
+#if defined(HAVE_STRCASECMP)
+  return !(strcasecmp)(first, second);
+#elif defined(HAVE_STRCMPI)
+  return !(strcmpi)(first, second);
+#elif defined(HAVE_STRICMP)
+  return !(stricmp)(first, second);
+#else
+  while(*first && *second) {
+    if(toupper(*first) != toupper(*second)) {
+      break;
+    }
+    first++;
+    second++;
+  }
+  return toupper(*first) == toupper(*second);
+#endif
+}
+
+/*
+ * @unittest: 1301
+ */
+int curl_strncasecompare(const char *first, const char *second, size_t max)
+{
+#if defined(HAVE_STRNCASECMP)
+  return !strncasecmp(first, second, max);
+#elif defined(HAVE_STRNCMPI)
+  return !strncmpi(first, second, max);
+#elif defined(HAVE_STRNICMP)
+  return !strnicmp(first, second, max);
+#else
+  while(*first && *second && max) {
+    if(toupper(*first) != toupper(*second)) {
+      break;
+    }
+    max--;
+    first++;
+    second++;
+  }
+  if(0 == max)
+    return 1; /* they are equal this far */
+
+  return toupper(*first) == toupper(*second);
+#endif
+}