Use better method to imply clap arguments.

As shown in <clap-rs/clap#4713>, instead of
`ArgPredicate::IsPresent` to detect `--basis-current`, it should be
`ArgPredicate::Equals("true".into())`.

This allows arbitrary ordering of clap arguments so that help text can
be ordered as desired.

README.md

@@ -186,9 +186,9 @@ Arguments:
 
 Options:
       --basis <BASIS>  choose alternate basis sequence number
+      --basis-current  choose basis to be current repository state
       --standalone     force ibundle to be standalone
       --allow-empty    allow creation of an empty ibundle
-      --basis-current  choose basis to be current repository state
   -q, --quiet          run quietly
   -h, --help           Print help information
   -V, --version        Print version information

src/main.rs

@@ -213,12 +213,16 @@ struct CreateArgs {
     #[arg(long)]
     basis: Option<SeqNum>,
 
+    /// choose basis to be current repository state
+    #[arg(long, conflicts_with("basis"))]
+    basis_current: bool,
+
     /// force ibundle to be standalone
     #[arg(
         long,
         default_value_if(
             "basis_current",
-            clap::builder::ArgPredicate::IsPresent,
+            clap::builder::ArgPredicate::Equals("true".into()),
             Some("true")
         )
     )]
@@ -229,16 +233,12 @@ struct CreateArgs {
         long,
         default_value_if(
             "basis_current",
-            clap::builder::ArgPredicate::IsPresent,
+            clap::builder::ArgPredicate::Equals("true".into()),
             Some("true")
         )
     )]
     allow_empty: bool,
 
-    /// choose basis to be current repository state
-    #[arg(long, conflicts_with("basis"))]
-    basis_current: bool,
-
     /// run quietly
     #[arg(short, long)]
     quiet: bool,