Make the c and ac scripts work with sh and without bin in PATH

Make the c and ac scripts work with sh and without bin in PATH

Make the bin/c and bin/ac scripts work with sh. The scripts are run with
/bin/sh shebang, which fails atleast on ubuntu 12.04 /bin/sh. The sh in
Ubuntu 12.04 is dash.

The fixes are according to the suggestions in http://mywiki.wooledge.org/Bashism

Also run "compare" script with explicit ./bin/ path to support people
who do not have skia/bin in PATH.

Committed: https://skia.googlesource.com/skia/+/c77f6af7c3ca08c94b882ccb2fbd61e6bae7ea42

[Kimmo Kinnunen, 2015-05-15 11:56:39]

kkinnunen@nvidia.com changed reviewers:
+ mtklein@google.com

[mtklein, 2015-05-15 12:29:59]

lgtm

[mtklein, 2015-05-15 12:30:04]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2015-05-15 12:30:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1139033005/1

[commit-bot: I haz the power, 2015-05-15 12:36:01]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/c77f6af7c3ca08c94b882ccb2fbd61e6bae7ea42