Weaken -U memory type check and move after config file parsing in main.c

The check for typos in -U memory names against a list of known memory names
now happens after the config files have been read, so newly declared memory
names can be considered. This commit also weakens the check against existence
of a known memory: it is now sufficent for a name to pass when it could be
the initial string of any known memory of any part. Any -U memory that cannot
possibly be matched up with a known memory is considered a typo and leads to
an exit before the programmer is opened.

This to protect users from typos that leave a device partially programmed.

When every -U memory name might be matching one of the known memories, the
programming is attempted. If the part to be programmed turns out not to have
a particular -U memory, AVRDUDE warns the user and skips this -U update.

This to support unifying interfaces that call AVRDUDE with potentially more
memories than the actual part has (eg, efuse on ATmega8).

src/main.c

@@ -751,6 +751,7 @@ int main(int argc, char * argv [])
     bitclock = default_bitclock;
   }
 
+
   avrdude_message(MSG_NOTICE, "\n");
 
   // developer option -p <wildcard>/[*codws] prints various aspects of part descriptions and exits
@@ -918,6 +919,12 @@ int main(int argc, char * argv [])
         exit(1);
       }
     }
+
+    if (!avr_mem_might_be_known(upd->memtype)) {
+      avrdude_message(MSG_INFO, "%s: unknown memory type %s\n", progname, upd->memtype);
+      exit(1);
+    }
+    // TODO: check whether filename other than "-" is readable/writable
   }
 
   /*