perforce: fix checksum

Closes #17841.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
pngcrush 1.7.50

Closes #17834.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
notmuch uses pkg-config

Closes #17833.
siege 2.74

Closes #17842.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
appengine-java-sdk 1.7.5

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
go appengine 32 1.7.5

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
go appengine 64 1.7.5

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
google appengine 1.7.5

Closes #17844.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
nginx 1.2.7, devel 1.3.12

Closes #17845.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
vim 7.3.820

Closes #17846.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
vimpager 1.7.9

Closes #17847.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
GitDownloadStrategy: split #fetch into several methods
GitDownloadStrategy: split up submodule update and checkout
GitDownloadStrategy: extract checkout from #stage
GitDownloadStrategy: only fetch from remote when necessary

When we are building from a tag, and that tag is already present in the
cached repository, we don't to hit the network; everything we need
already exists.
GitDownloadStrategy: quiet reset in non-verbose mode
GitDownloadStrategy: default to remote HEAD during checkout