make -k does not exit with appropriate error code if errors are encountered

[Max Khon]

Hi!

BSD make does not exit with appropriate error code (2) if it is run with 
"-k" and errors are encountered.

Please review this patch that fixes this bug:

http://people.freebsd.org/~fjoe/make.diff

Sample BSDmakefile is:

--- cut here ---
all:    a b

a:
         exit 1

b:
         touch ${.TARGET}
--- cut here ---

I'd like to commit the to HEAD soon.

/fjoe