Fix build with -Werror

Change-Id: I2fe4b006dc0696e5491792846bdb8c99ac31af6e
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Fix build with HarfBuzz-NG older than 0.9.20

It is annoying that HB maintains binary compatibility but does not
really care about source compatibility.

Change-Id: Ife7b011919f28527b77858ad8398fe723c65b1b3
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Clarify foreach's documentation on valued-containers

- Explain that values() is unnecessary and causes an extra copy.
- Replace "are fastest" with "are faster".
- Briefly explain the snippet.

Change-Id: Iff1d3a0b6140fca1d78157aeeca3d538c4d78b84
Reviewed-by: Albert Astals Cid <albert.astals@canonical.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>