Be less aggressive with CHMOD filesystem events

Be less aggressive with CHMOD filesystem events

On 4679fbee41d3, rebuild was disabled on
CHMOD filesystem events, but the code is overly aggressive.

In some situations, specially with older Mac's (using a Late 2008
Macbook), the events we receive might be aggregated. On my
particular laptop, I get this events:

    INFO: 2016/07/26 18:08:51 hugo.go:737: Received System Events: ["<path>": WRITE|CHMOD]

These events are ignored because the code only checks for Chmod. This
commit fixes this by checking that the event is also not a Write or Create.

Related to #1587.