t5310, t5510, t5516: adjust git fetch . in bare repositories

To avoid having to rely on implicit discovery of bare repositories
(which will go away at some stage by flipping the default of
`safe.bareRepository`), this commit replaces `-C <dir>` with
`--git-dir=<dir>`. Since `--git-dir` does not change the working
directory, a `.` that formerly referred to the `-C` target must become
`..` to reach the same location.

The code changes can be validated via this command-line:

  git diff HEAD^! | awk '
    /^diff/,/^\+\+\+/ { next }
    /^-/ { old[m++] = substr($0, 2) }
    /^\+/ {
      line = substr($0,2)
      # apply: -C X -> --git-dir=X and strip ../
      if (match(line, /--git-dir=(.* )\. /, a)) {
        gsub(/--git-dir=.* \. /, "-C " a[1] ".. ", line)
      }
      if (old[n++] != line) print old[n-1] " != " line
    }'

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

t/t5310-pack-bitmaps.sh

@@ -247,7 +247,7 @@ test_bitmap_cases () {
 		git commit -m "commit with big file" &&
 		git -c pack.packSizeLimit=500k repack -adb &&
 		git init --bare no-bitmaps.git &&
-		git -C no-bitmaps.git fetch .. HEAD
+		git --git-dir=no-bitmaps.git fetch . HEAD
 	'
 
 	test_expect_success 'set up reusable pack' '

t/t5510-fetch.sh

@@ -1375,7 +1375,7 @@ test_unpack_limit () {
 		git --bare init dest &&
 		git -C dest config fetch.unpacklimit $fetch_limit &&
 		git -C dest config transfer.unpacklimit $transfer_limit &&
-		git -C dest fetch .. onebranch &&
+		git --git-dir=dest fetch . onebranch &&
 		validate_store_type
 	'
 }

t/t5516-fetch-push.sh

@@ -1829,8 +1829,8 @@ test_expect_success 'refuse fetch to current branch of bare repository worktree'
 	git clone --bare . bare.git &&
 	git --git-dir=bare.git worktree add bare.git/wt &&
 	test_commit banana &&
-	test_must_fail git -C bare.git fetch .. HEAD:wt &&
-	git -C bare.git fetch -u .. HEAD:wt
+	test_must_fail git --git-dir=bare.git fetch . HEAD:wt &&
+	git --git-dir=bare.git fetch -u . HEAD:wt
 '
 
 test_expect_success 'refuse to push a hidden ref, and make sure do not pollute the repository' '