When a new FS image is created we need to calculate how much space each file is going to consume.
Fix two bugs in that logic:
- Count the space needed for indirection blocks for large files.
- Normally the trailing data of a file is written to a block of frag size, 4 kB by default.
However for files that use indirect blocks a full block is allocated, 32kB by default.
Take that into account.