Auto merge of #1682 - yoongkang:new_error_msg, r=alexcrichton

Some project names caused problems as
they already exist in target/debug. When
the projects fail to be created, the error
message was also not descriptive.

This commit adds a blacklist and a more
descriptive error message.

See #1618.

diff --cc src/cargo/util/toml.rs
Simple merge

diff --cc tests/test_cargo_compile.rs
Simple merge