libvtreefs: dynamically allocate long inode names

libvtreefs: dynamically allocate long inode names

Extended by David van Moolenbroek to continue using static buffers
for short inode names, so as to prevent important file system
services such as procfs from running out of memory at runtime.

Change-Id: I6f841741ee9944fc87dbdb78b5cdaa2abee9da76