Implement a dry run for -U updates before opening the programmer

This commit checks -U update requests for
  - Typos in memory names
  - Whether the files can be written or read
  - Automatic format detection if necessary

before opening the programmer. This to reduce the chances of the
programming failing midway through.

Minor additional changes:
  - Give strerror() system info when files are not read/writeable
  - Lift the auto detection message from MSG_INFO to MSG_NOTICE
  - Provide fileio_fmt_autodetect() in the AVRDUDE library
  - Rename fmtstr() in the AVRDUDE library to fileio_fmtstr() to
    avoid name clashes when an application links with it

Example:

$ avrdude -U - -U typo:r:.:h -U eeprom:w:testin:r -p ... -c ...
avrdude: can't auto detect file format for stdin/out, specify explicitly
avrdude: unknown memory type typo
avrdude: file . is not writeable (not a regular or character file?)
avrdude: file testin is not readable. No such file or directory

src/libavrdude.h

@@ -872,7 +872,9 @@ enum {
 extern "C" {
 #endif
 
-char * fmtstr(FILEFMT format);
+char * fileio_fmtstr(FILEFMT format);
+
+int fileio_fmt_autodetect(const char * fname);
 
 int fileio(int oprwv, char * filename, FILEFMT format,
            struct avrpart * p, char * memtype, int size);
@@ -936,6 +938,14 @@ const char *update_inname(const char *fn);
 const char *update_outname(const char *fn);
 const char *update_interval(int a, int b);
 
+// Helper functions for dry run to determine file access
+int update_is_okfile(const char *fn);
+int update_is_writeable(const char *fn);
+int update_is_readable(const char *fn);
+
+int update_dryrun(struct avrpart *p, UPDATE *upd);
+
+
 #ifdef __cplusplus
 }
 #endif