nco +netcdf4 extract failure when netcdf not installed

[ryandesign (Ryan Carsten Schmidt)]

If I try to extract nco with the netcdf4 variant but netcdf has not yet been installed, an error occurs:

$ sudo port extract nco +netcdf4
--->  Computing dependencies for nco
--->  Fetching nco
--->  Verifying checksum(s) for nco
--->  Extracting nco
Error: Target org.macports.extract returned: couldn't execute "/opt/local/bin/nc-config": no such file or directory
Error: Status 1 encountered during processing.

nco should not attempt to run nc-config, or anything else provided by a dependency, until the pre-configure phase; before that phase, the dependency may not yet have been installed.

[tenomoto (Takeshi Enomoto)]

Run nc-config in the pre-configure rather than the pre-extract phase. r64440