jiri: Better error when a project occurs in a different path than it is configured for.
jiri: Better error when a project occurs in a different path than it is configured for.

With this CL, Shyam would see this error rather than the more confusing
one he actually saw:

ERROR: project release.js.core has path /usr/local/google/home/nlacasse/code/v/release/javascript/core but was found in /usr/local/google/home/nlacasse/code/v/experimental/users/rosswang/bench/node_modules/vanadium
Change-Id: I62d5b1aa46e11e9befc83683293eca2f0facb966

vanadium/go.jiri,vanadium/go.jiri