save the recovery log from before HTC firmware updates

When doing a firmware (radio or hboot) update on HTC devices, save the
recovery log in block 1 of the cache partition, before the firmware
image and the UI bitmaps.  When we boot back into recovery after the
firmware update to reformat the cache partition, copy that log out of
cache before reformatting it and dump it into the current invocation's
log.

The practical upshot of all this is that we can see the log output
from radio and hboot updates.

Change-Id: Ie0e89566754c88f4bed6a90d8a0aa04047b01a27
diff --git a/bootloader.h b/bootloader.h
index 3d4302f..fec6409 100644
--- a/bootloader.h
+++ b/bootloader.h
@@ -54,6 +54,13 @@
 int write_update_for_bootloader(
         const char *update, int update_len,
         int bitmap_width, int bitmap_height, int bitmap_bpp,
-        const char *busy_bitmap, const char *error_bitmap);
+        const char *busy_bitmap, const char *error_bitmap,
+        const char *log_filename);
+
+/* Look for a log stored in the cache partition in the block after the
+ * firmware update header.  If we can read such a log, copy it to
+ * stdout (ie, the current log).
+ */
+void recover_firmware_update_log();
 
 #endif