brew.sh: rename 'chdir' to 'safe_cd'

This is inspired by `safe_system` with basically the same implication
(fail on error), making the name a lot less confusing and avoiding a
clash with the `chdir` function previously defined in `bin/brew`.

Closes #414.

Signed-off-by: Martin Afanasjew <martin@afanasjew.de>

Library/Homebrew/cmd/update.sh

@@ -311,7 +311,7 @@ EOS
   # only allow one instance of brew update
   lock update
 
-  chdir "$HOMEBREW_REPOSITORY"
+  safe_cd "$HOMEBREW_REPOSITORY"
   git_init_if_necessary
   # rename Taps directories
   # this procedure will be removed in the future if it seems unnecessary
@@ -382,7 +382,7 @@ EOS
     pull "$DIR"
   done
 
-  chdir "$HOMEBREW_REPOSITORY"
+  safe_cd "$HOMEBREW_REPOSITORY"
 
   if [[ -n "$HOMEBREW_UPDATED" ||
         -n "$HOMEBREW_UPDATE_FAILED" ||

Library/brew.sh

@@ -20,7 +20,7 @@ odie() {
   exit 1
 }
 
-chdir() {
+safe_cd() {
   cd "$@" >/dev/null || odie "Error: failed to cd to $*!"
 }