Add Google Cloud SQL support for App Engine.

It uses Cloud SQL as a database if it runs on Google App Engine with
using cloudsql DSN.

appengine.go includes a build constraint for Google App Engine (GAE)
(http://blog.golang.org/the-app-engine-sdk-and-workspaces-gopath) to
avoid an error outside App Engine and provide an exception. Using
Google Cloud SQL with App Engine GO SDK is not supported yet. It is a
SDK limitation.
Merge pull request #167 from dalinaum/cloudsql

Add Google Cloud SQL support for App Engine.
infile: lazy map init
infile: better buffer size calculation
infile: refactoring
infile: new deferredClose func instead of lambda funcs
Merge pull request #174 from go-sql-driver/infile

infile: refactoring
Comment typo
Merge pull request #175 from cxmcc/minor

Comment typo
fix #179
removed .Error() in logger, removed mutex to set logger
add CHANGELOG entry
Merge pull request #182 from arnehormann/configurable-logger

add a configurable logger
NUL-terminate old password scramble
DSN: check for separating slash

Fixes #186
Merge pull request #187 from go-sql-driver/dsn_trailingslash

DSN: check for separating slash
Merge pull request #188 from go-sql-driver/oldPasswords_fix

NUL-terminate old password scramble
ensure cipher memory safety
Merge pull request #190 from go-sql-driver/cipher_memsafe

ensure cipher memory safety
add test for scrambleOldPassword