Don't cache results from last file examined

- The filename was stored in a fixed-size buffer, which seems to be a rich
  source of security vulnerabilities

- The cache would incorrectly report no change when using a single temporary
  filename, with contents that vary over time

- It's of value only in very restricted situations: the only code that could
  take advantage of the cache is something that's repeatedly loading the
  same file, without loading any other files in between

Given the latter point, it doesn't seem worth fixing the first two issues.

Image-EXIF.xs

@@ -14,26 +14,16 @@ unsigned short dumplvl = 0;
 static int
 read_data(char *name)
 {
-    static char prev_name[1024] = "";
-
     int mark, first = 0;
     unsigned int len, rlen;
     unsigned char *exifbuf = NULL;
+    FILE *fp = fopen(name, "rb");
 
-    FILE *fp;
-
-    if (strcmp(name, prev_name) == 0)
-        return 0;
-
-    fp = fopen(name, "rb");
     if (!fp) {
-        prev_name[0] = '\0';
         exifdie((const char *)strerror(errno));
         return 2;
     }
 
-    strcpy(prev_name, name);
-
     while (jpegscan(fp, &mark, &len, !(first++))) {
         if (mark != JPEG_M_APP1) {
             if (fseek(fp, len, SEEK_CUR)) {