zshrc: don't set tabs.

Setting the tabs to a nonstandard value causes problems with the version
of htop in EPEL 6, and it causes machines I ssh into that don't have my
shell configuration to have broken formatting of ls results.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
vim: add highlighting for more C types.

Identifiers ending in "_t" are traditionally typedefs in C.  Highlight
them as such.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>