Add hidden interface to support FeOS implementation of multiple cwd.

This interface grabs the pointer to the cwd cluster. This interface
is hidden because it can be very easily used incorrectly. Modifying
the cwd cluster value may cause unexpected results, so use at your
own risk, which includes a corrupted storage medium.

include/fat.h

@@ -113,6 +113,7 @@ Methods to modify DOS File Attributes
 int	FAT_getAttr(const char *file);
 int	FAT_setAttr(const char *file, int attr );
 
+#define LIBFAT_FEOS_MULTICWD
 
 #ifdef __cplusplus
 }

source/partition.c

@@ -429,3 +429,13 @@ void _FAT_partition_writeFSinfo(PARTITION * partition)
 	_FAT_disc_writeSectors (partition->disc, partition->fsInfoSector, 1, sectorBuffer);
 	_FAT_mem_free(sectorBuffer);
 }
+
+uint32_t* _FAT_getCwdClusterPtr(const char* name) {
+	PARTITION *partition = _FAT_partition_getPartitionFromPath(name);
+
+	if (!partition) {
+		return NULL;
+	}
+
+	return &partition->cwdCluster;
+}