Remove an extra slash that ends up in the metalog. This double slash
can produce an invalid specification file if there are subdirectories
down the hierarchy when sorted.
For example, consider the following metalog excerpt:
./base/aaa type=dir ./base//aaa/bbb type=dir
If sorted, would turn out:
./base//aaa/bbb type=dir ./base/aaa type=dir
Apparently missing the ./base/aaa directory in the specification.
Luckily here are no subdirectories.