Auto merge of #4831 - str4d:shell-cleanups, r=daira

Shell script cleanups

Cherry-picked from https://github.com/bitcoin/bitcoin/pull/10773.

Fixes a bug with `./contrib/devtools/gen-manpages.sh` backported in zcash/zcash#4827.

contrib/devtools/gen-manpages.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 
 export LC_ALL=C
 TOPDIR=${TOPDIR:-$(git rev-parse --show-toplevel)}

contrib/tidy_datadir.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 
 if [ -d "$1" ]; then
-  cd "$1"
+  cd "$1" || exit 1
 else
   echo "Usage: $0 <datadir>" >&2
   echo "Removes obsolete Bitcoin database files" >&2

share/genbuild.sh

@@ -7,7 +7,7 @@
 
 export LC_ALL=C
 if [ $# -gt 1 ]; then
-    cd "$2"
+    cd "$2" || exit 1
 fi
 if [ $# -gt 0 ]; then
     FILE="$1"