Better regexes for path determination.

On further examination it looks like this is a better regex to use; it works in all cases that I could think of. A sample session from debugging this follows:

```ruby
irb(main):033:0> value
=> "test/thing"
irb(main):034:0> ((value =~ /^[^\/]/) == 0) or ((value =~ %r{/\.\./}) == 0)
=> true
irb(main):035:0> value = '../test'
=> "../test"
irb(main):036:0> ((value =~ /^[^\/]/) == 0) or ((value =~ %r{/\.\./}) == 0)
=> true
irb(main):037:0> value = '/var/lib/pg/data'
=> "/var/lib/pg/data"
irb(main):038:0> ((value =~ /^[^\/]/) == 0) or ((value =~ %r{/\.\./}) == 0)
=> false
irb(main):039:0> value = './var/lib/pg/data'
=> "./var/lib/pg/data"
irb(main):040:0> ((value =~ /^[^\/]/) == 0) or ((value =~ %r{/\.\./}) == 0)
=> true
```