When reading from a file, default to writing to stdout.

- Change `sq key revoke`, `sq key userid revoke`, and `sq key subkey
    revoke` to default to writing to stdout when reading from a file.

src/commands/key/revoke.rs

@@ -9,6 +9,7 @@ use openpgp::Result;
 
 use crate::Sq;
 use crate::cli::key::RevokeCommand;
+use crate::cli::types::FileOrStdout;
 use crate::common::RevocationOutput;
 use crate::common::get_secret_signer;
 use crate::parse_notations;
@@ -85,9 +86,15 @@ impl RevocationOutput for CertificateRevocation
 /// Revoke a certificate
 pub fn certificate_revoke(
     sq: Sq,
-    command: RevokeCommand,
+    mut command: RevokeCommand,
 ) -> Result<()> {
     let cert = if let Some(file) = command.cert_file {
+        if command.output.is_none() {
+            // None means to write to the cert store.  When reading
+            // from a file, we want to write to stdout by default.
+            command.output = Some(FileOrStdout::new(None));
+        }
+
         let br = file.open()?;
         Cert::from_buffered_reader(br)?
     } else if let Some(kh) = command.cert {

src/commands/key/subkey.rs

@@ -20,6 +20,7 @@ use crate::cli::key::SubkeyAddCommand;
 use crate::cli::key::SubkeyCommand;
 use crate::cli::key::SubkeyRevokeCommand;
 use crate::cli::types::EncryptPurpose;
+use crate::cli::types::FileOrStdout;
 use crate::common;
 use crate::common::NULL_POLICY;
 use crate::common::RevocationOutput;
@@ -223,9 +224,15 @@ fn subkey_add(
 /// revocation fails.
 pub fn subkey_revoke(
     sq: Sq,
-    command: SubkeyRevokeCommand,
+    mut command: SubkeyRevokeCommand,
 ) -> Result<()> {
     let cert = if let Some(file) = command.cert_file {
+        if command.output.is_none() {
+            // None means to write to the cert store.  When reading
+            // from a file, we want to write to stdout by default.
+            command.output = Some(FileOrStdout::new(None));
+        }
+
         let br = file.open()?;
         Cert::from_buffered_reader(br)?
     } else if let Some(kh) = command.cert {

src/commands/key/userid.rs

@@ -396,9 +396,15 @@ signatures on other User IDs to make the key valid again.",
 /// [`NotationData`] fails or if the eventual revocation fails.
 pub fn userid_revoke(
     sq: Sq,
-    command: UseridRevokeCommand,
+    mut command: UseridRevokeCommand,
 ) -> Result<()> {
     let cert = if let Some(file) = command.cert_file {
+        if command.output.is_none() {
+            // None means to write to the cert store.  When reading
+            // from a file, we want to write to stdout by default.
+            command.output = Some(FileOrStdout::new(None));
+        }
+
         let br = file.open()?;
         Cert::from_buffered_reader(br)?
     } else if let Some(kh) = command.cert {