add support for microsecond periods (GH2145)

(Continues #2145)

Alrighty. This should be fine. There may be a few formatting changes that I rolled back through the git diff / apply patch, but all not-skipped tests pass so I figured it wasn't a big deal. Here's what I did to fix the problem, which was continually merging with upstream:

```shell
function get_my_commits {
    local curdir="$(pwd)"
    cd "$1"
    # %n adds a newline in addition to the file name
    # sed removes blank lines here
    # sort -u sorts and removes duplicates lines
    git log --name-only --pretty=%n --author=Phillip 0eeff..master | sort -u | sed '/^$/d' 
}

old_pandas=/path/to/evil/pandas/merge/of/death
new_pandas=/shiny/new/checkout/of/pandas

get_my_commits $old_pandas | while read file; do
    # some boolean tests to filter out setup.py and missing files between versions
    diff -pu "$old_pandas/$file" "$new_pandas/$file" | patch -p0 "$new_pandas/$file"
done
```
Needless to say I won't be doing any more merging of upstream into my branch. Thanks to those who helped me out here.