Enhanced error message in verify_sdp.sh if p4d_N script is malformed.
The /p4/N/bin/p4d_N only exists as a script for case-insensitive
servers. Normally this file is generated (by mkdirs.sh), but in
some DIY installations it may be handcrafted, and possibly wrong.
This changes improves the error message in that scenario, such that
the user has enough information to correct the problem.
This also fixes a funky formatting issue when the error occurred.