This patch fixes a situation in which vdump would exit 
with message "Not enough memory to generate link table".

The problem is caused by introduction of hash table in PK4 vdump. 
The table is used to keep track of the hard links during dump.
Vdump maintained inode structures for all the inodes encountered. 
Also, each inode structure maintained path_name which is of 
size 1024 byte.

The problem is now fixed by, 
1. maintaining inode structures only for inodes 
   which has link count >1 (hard links);
2. inode structures no more maintain expensive path_name 
   which is not required.

The functionality of vdump to estimate correct bytes_to_backup 
in case of hard links, and report any missed hard links in case 
of directory level backup, is maintained.


