.gitignore: fix attempt at rooted paths
.gitignore: fix attempt at rooted paths

When I wrote the lines

	bin/
	pkg/

I was trying to match just the top-level bin and pkg directories, and I put the
final slash in because 'git help gitignore' says:

       o   If the pattern does not contain a slash /, Git treats it as a shell
           glob pattern and checks for a match against the pathname relative
           to the location of the .gitignore file (relative to the toplevel of
           the work tree if not from a .gitignore file).

       o   Otherwise, Git treats the pattern as a shell glob suitable for
           consumption by fnmatch(3) with the FNM_PATHNAME flag: wildcards in
           the pattern will not match a / in the pathname. For example,
           "Documentation/*.html" matches "Documentation/git.html" but not
           "Documentation/ppc/ppc.html" or
           "tools/perf/Documentation/perf.html".

Putting a trailing slash was my way of opting in to the "rooted path" semantics
without looking different from the surrounding rooted paths like "src/go/build/zcgo.go".

But HA HA GIT FOOLED YOU! above those two bullets the docs say:

       o   If the pattern ends with a slash, it is removed for the purpose of
           the following description, ...

Change all the patterns to use a leading slash for "rooted" behavior.

This bit me earlier today because I had a perfectly reasonable source
code directory go/src/cmd/go/testdata/src/empty/pkg that was
not added by 'git add empty'.

Change-Id: I6f8685b3c5be22029c33de9ccd735487089a1c03
Reviewed-on: https://go-review.googlesource.com/34832
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

codestation/go,akutz/go,vsekhar/elastic-go,josharian/go,codestation/go,derekmarcotte/go,ImJasonH/go,polyverse-security/go,CAFxX/go,Cofyc/go,linux-on-ibm-z/go,derekmarcotte/go,Cofyc/go,polyverse-security/go,Cofyc/go,polyverse-security/go,suncycheng/go,nawawi/go,cloudflare/go,Cofyc/go,akutz/go,linux-on-ibm-z/go,akutz/go,vsekhar/elastic-go,polyverse-security/go,polyverse-security/go,vsekhar/elastic-go,derekmarcotte/go,polyverse-security/go,suncycheng/go,cloudflare/go,CAFxX/go,derekmarcotte/go,vsekhar/elastic-go,vsekhar/elastic-go,codestation/go,derekmarcotte/go,cloudflare/go,nawawi/go,linux-on-ibm-z/go,suncycheng/go,CAFxX/go,ImJasonH/go,ImJasonH/go,nawawi/go,CAFxX/go,ImJasonH/go,vsekhar/elastic-go,CAFxX/go,nawawi/go,nawawi/go,suncycheng/go,codestation/go,codestation/go,akutz/go,akutz/go,suncycheng/go,linux-on-ibm-z/go,nawawi/go,josharian/go,golang/go,golang/go,vsekhar/elastic-go,suncycheng/go,linux-on-ibm-z/go,CAFxX/go,cloudflare/go,CAFxX/go,josharian/go,suncycheng/go,linux-on-ibm-z/go,CAFxX/go,josharian/go,derekmarcotte/go,linux-on-ibm-z/go,josharian/go,suncycheng/go,linux-on-ibm-z/go,vsekhar/elastic-go,polyverse-security/go,codestation/go,cloudflare/go,cloudflare/go,golang/go,akutz/go,golang/go,cloudflare/go,ImJasonH/go,ImJasonH/go,derekmarcotte/go,ImJasonH/go,golang/go,derekmarcotte/go,nawawi/go,Cofyc/go,cloudflare/go,josharian/go,ImJasonH/go,nawawi/go,codestation/go,polyverse-security/go,golang/go,josharian/go,christopher-henderson/Go,Cofyc/go,codestation/go,akutz/go,josharian/go,golang/go,golang/go,Cofyc/go,akutz/go,Cofyc/go