Add strndup.h header so we can use this useful function

It's missing on Windows... we had this helper in liquivision.c but since I
used the function in git-access.c I figured I should just turn it into a
little helper.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

git-access.c

@@ -12,6 +12,7 @@
 
 #include "dive.h"
 #include "membuffer.h"
+#include "strndup.h"
 
 /*
  * The libgit2 people are incompetent at making libraries. They randomly change

liquivision.c

@@ -3,7 +3,7 @@
 #include "dive.h"
 #include "divelist.h"
 #include "file.h"
-
+#include "strndup.h"
 
 // Convert bytes into an INT
 #define array_uint16_le(p) ((unsigned int) (p)[0] \
@@ -12,21 +12,6 @@
 							+ ((p)[1]<<8) + ((p)[2]<<16) \
 							+ ((p)[3]<<24))
 
-#if __WIN32__
-static char *strndup (const char *s, size_t n)
-{
-	char *cpy;
-	size_t len = strlen(s);
-	if (n < len)
-		len = n;
-	if ((cpy = malloc(len + 1)) != NULL) {
-		cpy[len] = '\0';
-		memcpy(cpy, s, len);
-	}
-	return cpy;
-}
-#endif
-
 struct lv_event {
 	time_t time;
 	struct pressure {

save-xml.c

@@ -10,6 +10,7 @@
 #include "dive.h"
 #include "device.h"
 #include "membuffer.h"
+#include "strndup.h"
 
 /*
  * We're outputting utf8 in xml.
@@ -45,9 +46,7 @@ static void show_utf8(struct membuffer *b, const char *text, const char *pre, co
 		return;
 	while (len && isascii(text[len - 1]) && isspace(text[len - 1]))
 		len--;
-	/* strndup would be easier, but that doesn't appear to exist on Windows / Mac */
-	cleaned = strdup(text);
-	cleaned[len] = '\0';
+	cleaned = strndup(text, len);
 	put_string(b, pre);
 	quote(b, cleaned, is_attribute);
 	put_string(b, post);

strndup.h

@@ -0,0 +1,21 @@
+#ifndef STRNDUP_H
+#define STRNDUP_H
+#if __WIN32__
+static char *strndup (const char *s, size_t n)
+{
+	char *cpy;
+	size_t len = strlen(s);
+	if (n < len)
+		len = n;
+	if ((cpy = malloc(len + 1)) !=
+	    NULL) {
+		cpy[len] =
+				'\0';
+		memcpy(cpy,
+		       s,
+		       len);
+	}
+	return cpy;
+}
+#endif
+#endif /* STRNDUP_H */