Make node-canvas compile with libjpeg62-dev or libjpeg8-dev.

- detect if libjpeg is < 8 and if so, define our own jpeg_mem_src.

src/Image.cc

@@ -14,6 +14,7 @@
 
 #ifdef HAVE_JPEG
 #include <jpeglib.h>
+#include <jerror.h>
 #endif
 
 #ifdef HAVE_GIF
@@ -547,6 +548,45 @@ Image::loadGIFFromBuffer(uint8_t *buf, unsigned len) {
 
 #ifdef HAVE_JPEG
 
+// libjpeg 6.2 does not have jpeg_mem_src; define it ourselves here unless
+// libjpeg 8 is installed.
+#if JPEG_LIB_VERSION < 80
+
+/* Read JPEG image from a memory segment */
+static void init_source (j_decompress_ptr cinfo) {}
+static boolean fill_input_buffer (j_decompress_ptr cinfo) {
+  ERREXIT(cinfo, JERR_INPUT_EMPTY);
+  return TRUE;
+}
+static void skip_input_data (j_decompress_ptr cinfo, long num_bytes) {
+  struct jpeg_source_mgr* src = (struct jpeg_source_mgr*) cinfo->src;
+  if (num_bytes > 0) {
+    src->next_input_byte += (size_t) num_bytes;
+    src->bytes_in_buffer -= (size_t) num_bytes;
+  }
+}
+static void term_source (j_decompress_ptr cinfo) {}
+static void jpeg_mem_src (j_decompress_ptr cinfo, void* buffer, long nbytes) {
+  struct jpeg_source_mgr* src;
+
+  if (cinfo->src == NULL) {   /* first time for this JPEG object? */
+    cinfo->src = (struct jpeg_source_mgr *)
+      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
+                                  sizeof(struct jpeg_source_mgr));
+  }
+
+  src = (struct jpeg_source_mgr*) cinfo->src;
+  src->init_source = init_source;
+  src->fill_input_buffer = fill_input_buffer;
+  src->skip_input_data = skip_input_data;
+  src->resync_to_restart = jpeg_resync_to_restart; /* use default method */
+  src->term_source = term_source;
+  src->bytes_in_buffer = nbytes;
+  src->next_input_byte = (JOCTET*)buffer;
+}
+
+#endif
+
 /*
  * Load jpeg from buffer.
  */