testlib: move the prune alias into a shell script for Windows

Cramming all of this directly into an alias doesn't play nicely on Windows.
Various test-exchange-obsmarkers-case-XX.t were failing with:

    abort: cannot select revision when creating marker

It turned out that inside debugcommands.debugobsolete(), the following differed
from Linux (where they were empty, at least in the case I debugged):

    'rev': ['.`;'],
    'template': "'{node}\\n'"

tests/testlib/exchange-obsmarker-util.sh

@@ -1,133 +1,139 b''
 #!/bin/sh
 # setup config and various utility to test obsolescence marker exchanges tests
 
+cat >> $TESTTMP/prune.sh << EOF
+rev=\`hg log --hidden --template '{node}\n' --rev "\$3"\`
+
+hg debugobsolete --record-parents \$1 "\$2" \$rev \
+   && hg up --quiet 'max((::.) - obsolete())'
+EOF
+
 cat >> $HGRCPATH <<EOF
 [web]
 # We test http pull and push, drop authentication requirement
 push_ssl = false
 allow_push = *
 
 [ui]
 # simpler log output
 logtemplate ="{node|short} ({phase}): {desc}\n"
 
 [phases]
 # non publishing server
 publish=False
 
 [experimental]
 # reduce output changes
 bundle2-output-capture=True
 # enable evolution
 evolution=all
 
 [extensions]
 # we need to strip some changeset for some test cases
 hgext.strip=
 
 [alias]
 # fix date used to create obsolete markers.
 debugobsolete=debugobsolete -d '0 0'
 # poor man substiture to the evolve 'hg prune'. using prune makes the test clearer and 
-prune =!hg debugobsolete --record-parents \$1 "\$2" \`hg log --hidden --template '{node}\n' --rev "\$3"\`;\
-        hg up --quiet 'max((::.) - obsolete())'
+prune = !sh $TESTTMP/prune.sh \$1 "\$2" "\$3"
 EOF
 
 mkcommit() {
    echo "$1" > "$1"
    hg add "$1"
    hg ci -m "$1"
 }
 getid() {
    hg log --hidden --template '{node}\n' --rev "$1"
 }
 
 setuprepos() {
     echo creating test repo for test case $1
     mkdir $1
     cd $1
     echo - pulldest
     hg init pushdest
     cd pushdest
     mkcommit O
     hg phase --public .
     cd ..
     echo - main
     hg clone -q pushdest main
     echo - pushdest
     hg clone -q main pulldest
     echo 'cd into `main` and proceed with env setup'
 }
 
 inspect_obsmarkers (){
     # This exist as its own function to help the evolve extension reuse the tests as is.
     # The evolve extensions version will includes more advances query (eg:
     # related to obsmarkers discovery) to this.
     echo 'obsstore content'
     echo '================'
     hg debugobsolete
 }
 
 dotest() {
     # dotest TESTNAME [TARGETNODE] [PUSHFLAGS+]
     #
     # test exchange for the given test case.
     #
     # This function performs push and pull in all directions through all
     # protocols and display the resulting obsolescence markers on all sides.
 
     testcase=$1
     shift
     target="$1"
     if [ $# -gt 0 ]; then
         shift
     fi
     targetnode=""
     desccall=""
     cd $testcase
     echo "## Running testcase $testcase"
     if [ -n "$target" ]; then
         desccall="desc("\'"$target"\'")"
         targetnode="`hg -R main id -qr \"$desccall\"`"
         echo "# testing echange of \"$target\" ($targetnode)"
     fi
     echo "## initial state"
     echo "# obstore: main"
     hg -R main     debugobsolete | sort
     echo "# obstore: pushdest"
     hg -R pushdest debugobsolete | sort
     echo "# obstore: pulldest"
     hg -R pulldest debugobsolete | sort
 
     if [ -n "$target" ]; then
         echo "## pushing \"$target\"" from main to pushdest
         hg -R main push -r "$desccall" $@ pushdest
     else
         echo "## pushing from main to pushdest"
         hg -R main push pushdest $@
     fi
     echo "## post push state"
     echo "# obstore: main"
     hg -R main     debugobsolete | sort
     echo "# obstore: pushdest"
     hg -R pushdest debugobsolete | sort
     echo "# obstore: pulldest"
     hg -R pulldest debugobsolete | sort
     if [ -n "$target" ]; then
         echo "## pulling \"$targetnode\"" from main into pulldest
         hg -R pulldest pull -r $targetnode $@ main
     else
         echo "## pulling from main into pulldest"
         hg -R pulldest pull main $@
     fi
     echo "## post pull state"
     echo "# obstore: main"
     hg -R main     debugobsolete | sort
     echo "# obstore: pushdest"
     hg -R pushdest debugobsolete | sort
     echo "# obstore: pulldest"
     hg -R pulldest debugobsolete | sort
 
     cd ..
 
 }