header files

[Ross Paterson]

In 4.1.1, we have

	impent -> " [static] [fname] [&] [cid] "

so we can specify at most one header file.  How about changing that to

	impent -> " [static] {fname} [&] [cid] "

so we can have any number?  I know this isn't essential (because I can
create a header file containing #include's) but it would be convenient.