.gitignore: also ignore tahoe-deps and .tgz, to fix 'make tarballs'

Otherwise, the get-version-from-git code thinks the tree is dirty, and
creates SUMO tarballs with -dirty in the name.

TAG allmydata-tahoe-1.9.0

TAG allmydata-tahoe-1.9.0b1

TAG allmydata-tahoe-1.9.0a2

TAG allmydata-tahoe-1.9.0a1

Fix repeated 'the' in license text.

mutable/layout.py: fix unused import. refs tahoe-lafs#393

test/test_mutable: test for incorrect div_ceil equations

update docs for the 1.8.2 release

TAG allmydata-tahoe-1.8.2